X-Git-Url: http://nitlanguage.org

diff --git a/c_src/poset.sep.1.c b/c_src/poset.sep.1.c
index 0ee3068..9e04dd7 100644
--- a/c_src/poset.sep.1.c
+++ b/c_src/poset.sep.1.c
@@ -1,18 +1,18 @@
 #include "poset.sep.0.h"
-/* method poset#POSet#iterator for (self: POSet[Object]): Iterator[Object] */
-val* poset__POSet__iterator(val* self) {
-val* var /* : Iterator[Object] */;
-val* var1 /* : HashMap[Object, POSetElement[Object]] */;
-val* var3 /* : HashMap[Object, POSetElement[Object]] */;
-val* var4 /* : RemovableCollection[Object] */;
-val* var6 /* : RemovableCollection[Object] */;
+/* method poset#POSet#iterator for (self: POSet[nullable Object]): Iterator[nullable Object] */
+val* poset___poset__POSet___standard__abstract_collection__Collection__iterator(val* self) {
+val* var /* : Iterator[nullable Object] */;
+val* var1 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+val* var3 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+val* var4 /* : RemovableCollection[nullable Object] */;
+val* var6 /* : RemovableCollection[nullable Object] */;
 val* var7 /* : Iterator[nullable Object] */;
 {
-{ /* Inline poset#POSet#elements (self) on <self:POSet[Object]> */
-var3 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[Object]> */
+{ /* Inline poset#POSet#elements (self) on <self:POSet[nullable Object]> */
+var3 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[nullable Object]> */
 if (unlikely(var3 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _elements");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 33);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 82);
 show_backtrace(1);
 }
 var1 = var3;
@@ -20,11 +20,11 @@ RET_LABEL2:(void)0;
 }
 }
 {
-{ /* Inline hash_collection#HashMap#keys (var1) on <var1:HashMap[Object, POSetElement[Object]]> */
-var6 = var1->attrs[COLOR_hash_collection__HashMap___keys].val; /* _keys on <var1:HashMap[Object, POSetElement[Object]]> */
+{ /* Inline hash_collection#HashMap#keys (var1) on <var1:HashMap[nullable Object, POSetElement[nullable Object]]> */
+var6 = var1->attrs[COLOR_standard__hash_collection__HashMap___keys].val; /* _keys on <var1:HashMap[nullable Object, POSetElement[nullable Object]]> */
 if (unlikely(var6 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _keys");
-PRINT_ERROR(" (%s:%d)\n", "../lib/standard/collection/hash_collection.nit", 249);
+PRINT_ERROR(" (%s:%d)\n", FILE_standard__hash_collection, 275);
 show_backtrace(1);
 }
 var4 = var6;
@@ -32,92 +32,70 @@ RET_LABEL5:(void)0;
 }
 }
 {
-var7 = ((val* (*)(val*))(var4->class->vft[COLOR_abstract_collection__Collection__iterator]))(var4) /* iterator on <var4:RemovableCollection[Object]>*/;
+var7 = ((val* (*)(val* self))(var4->class->vft[COLOR_standard__abstract_collection__Collection__iterator]))(var4) /* iterator on <var4:RemovableCollection[nullable Object]>*/;
 }
 var = var7;
 goto RET_LABEL;
 RET_LABEL:;
 return var;
 }
-/* method poset#POSet#iterator for (self: Object): Iterator[nullable Object] */
-val* VIRTUAL_poset__POSet__iterator(val* self) {
-val* var /* : Iterator[nullable Object] */;
-val* var1 /* : Iterator[Object] */;
-var1 = poset__POSet__iterator(self);
-var = var1;
-RET_LABEL:;
-return var;
-}
-/* method poset#POSet#elements for (self: POSet[Object]): HashMap[Object, POSetElement[Object]] */
-val* poset__POSet__elements(val* self) {
-val* var /* : HashMap[Object, POSetElement[Object]] */;
-val* var1 /* : HashMap[Object, POSetElement[Object]] */;
-var1 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[Object]> */
+/* method poset#POSet#elements for (self: POSet[nullable Object]): HashMap[nullable Object, POSetElement[nullable Object]] */
+val* poset___poset__POSet___elements(val* self) {
+val* var /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+val* var1 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+var1 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[nullable Object]> */
 if (unlikely(var1 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _elements");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 33);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 82);
 show_backtrace(1);
 }
 var = var1;
 RET_LABEL:;
 return var;
 }
-/* method poset#POSet#elements for (self: Object): HashMap[Object, POSetElement[Object]] */
-val* VIRTUAL_poset__POSet__elements(val* self) {
-val* var /* : HashMap[Object, POSetElement[Object]] */;
-val* var1 /* : HashMap[Object, POSetElement[Object]] */;
-val* var3 /* : HashMap[Object, POSetElement[Object]] */;
-{ /* Inline poset#POSet#elements (self) on <self:Object(POSet[Object])> */
-var3 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:Object(POSet[Object])> */
-if (unlikely(var3 == NULL)) {
-PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _elements");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 33);
-show_backtrace(1);
-}
-var1 = var3;
-RET_LABEL2:(void)0;
-}
-var = var1;
-RET_LABEL:;
-return var;
-}
-/* method poset#POSet#has for (self: POSet[Object], Object): Bool */
-short int poset__POSet__has(val* self, val* p0) {
+/* method poset#POSet#has for (self: POSet[nullable Object], nullable Object): Bool */
+short int poset___poset__POSet___standard__abstract_collection__Collection__has(val* self, val* p0) {
 short int var /* : Bool */;
 short int var1 /* : Bool */;
 int cltype;
 int idtype;
 const struct type* type_struct;
+short int is_nullable;
 const char* var_class_name;
-val* var_e /* var e: Object */;
-val* var2 /* : HashMap[Object, POSetElement[Object]] */;
-val* var4 /* : HashMap[Object, POSetElement[Object]] */;
-val* var5 /* : RemovableCollection[Object] */;
-val* var7 /* : RemovableCollection[Object] */;
+val* var_e /* var e: nullable Object */;
+val* var2 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+val* var4 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+val* var5 /* : RemovableCollection[nullable Object] */;
+val* var7 /* : RemovableCollection[nullable Object] */;
 short int var8 /* : Bool */;
-/* Covariant cast for argument 0 (e) <p0:Object> isa E */
-/* <p0:Object> isa E */
-type_struct = self->type->resolution_table->types[COLOR_abstract_collection__Collection_FT0];
+/* Covariant cast for argument 0 (e) <p0:nullable Object> isa E */
+/* <p0:nullable Object> isa E */
+type_struct = self->type->resolution_table->types[COLOR_poset__POSet___35dE];
 cltype = type_struct->color;
 idtype = type_struct->id;
+is_nullable = type_struct->is_nullable;
+if(p0 == NULL) {
+var1 = is_nullable;
+} else {
 if(cltype >= p0->type->table_size) {
 var1 = 0;
 } else {
 var1 = p0->type->type_table[cltype] == idtype;
 }
+}
 if (unlikely(!var1)) {
 var_class_name = p0 == NULL ? "null" : p0->type->name;
 PRINT_ERROR("Runtime error: Cast failed. Expected `%s`, got `%s`", "E", var_class_name);
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 36);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 85);
 show_backtrace(1);
 }
 var_e = p0;
 {
-{ /* Inline poset#POSet#elements (self) on <self:POSet[Object]> */
-var4 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[Object]> */
+{ /* Inline poset#POSet#elements (self) on <self:POSet[nullable Object]> */
+var4 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[nullable Object]> */
 if (unlikely(var4 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _elements");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 33);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 82);
 show_backtrace(1);
 }
 var2 = var4;
@@ -125,11 +103,11 @@ RET_LABEL3:(void)0;
 }
 }
 {
-{ /* Inline hash_collection#HashMap#keys (var2) on <var2:HashMap[Object, POSetElement[Object]]> */
-var7 = var2->attrs[COLOR_hash_collection__HashMap___keys].val; /* _keys on <var2:HashMap[Object, POSetElement[Object]]> */
+{ /* Inline hash_collection#HashMap#keys (var2) on <var2:HashMap[nullable Object, POSetElement[nullable Object]]> */
+var7 = var2->attrs[COLOR_standard__hash_collection__HashMap___keys].val; /* _keys on <var2:HashMap[nullable Object, POSetElement[nullable Object]]> */
 if (unlikely(var7 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _keys");
-PRINT_ERROR(" (%s:%d)\n", "../lib/standard/collection/hash_collection.nit", 249);
+PRINT_ERROR(" (%s:%d)\n", FILE_standard__hash_collection, 275);
 show_backtrace(1);
 }
 var5 = var7;
@@ -137,73 +115,70 @@ RET_LABEL6:(void)0;
 }
 }
 {
-var8 = ((short int (*)(val*, val*))(var5->class->vft[COLOR_abstract_collection__Collection__has]))(var5, var_e) /* has on <var5:RemovableCollection[Object]>*/;
+var8 = ((short int (*)(val* self, val* p0))(var5->class->vft[COLOR_standard__abstract_collection__Collection__has]))(var5, var_e) /* has on <var5:RemovableCollection[nullable Object]>*/;
 }
 var = var8;
 goto RET_LABEL;
 RET_LABEL:;
 return var;
 }
-/* method poset#POSet#has for (self: Object, nullable Object): Bool */
-short int VIRTUAL_poset__POSet__has(val* self, val* p0) {
-short int var /* : Bool */;
-short int var1 /* : Bool */;
-var1 = poset__POSet__has(self, p0);
-var = var1;
-RET_LABEL:;
-return var;
-}
-/* method poset#POSet#add_node for (self: POSet[Object], Object): POSetElement[Object] */
-val* poset__POSet__add_node(val* self, val* p0) {
-val* var /* : POSetElement[Object] */;
+/* method poset#POSet#add_node for (self: POSet[nullable Object], nullable Object): POSetElement[nullable Object] */
+val* poset___poset__POSet___add_node(val* self, val* p0) {
+val* var /* : POSetElement[nullable Object] */;
 short int var1 /* : Bool */;
 int cltype;
 int idtype;
 const struct type* type_struct;
+short int is_nullable;
 const char* var_class_name;
-val* var_e /* var e: Object */;
-val* var2 /* : HashMap[Object, POSetElement[Object]] */;
-val* var4 /* : HashMap[Object, POSetElement[Object]] */;
-val* var5 /* : RemovableCollection[Object] */;
-val* var7 /* : RemovableCollection[Object] */;
+val* var_e /* var e: nullable Object */;
+val* var2 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+val* var4 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+val* var5 /* : RemovableCollection[nullable Object] */;
+val* var7 /* : RemovableCollection[nullable Object] */;
 short int var8 /* : Bool */;
-val* var9 /* : HashMap[Object, POSetElement[Object]] */;
-val* var11 /* : HashMap[Object, POSetElement[Object]] */;
+val* var9 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+val* var11 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
 val* var12 /* : nullable Object */;
-val* var13 /* : POSetElement[Object] */;
-val* var14 /* : HashMap[Object, POSetElement[Object]] */;
-val* var16 /* : HashMap[Object, POSetElement[Object]] */;
+val* var13 /* : POSetElement[nullable Object] */;
+val* var14 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+val* var16 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
 long var17 /* : Int */;
-val* var_poe /* var poe: POSetElement[Object] */;
-val* var18 /* : HashSet[Object] */;
-val* var20 /* : HashSet[Object] */;
-val* var21 /* : HashSet[Object] */;
-val* var23 /* : HashSet[Object] */;
-val* var24 /* : HashMap[Object, POSetElement[Object]] */;
-val* var26 /* : HashMap[Object, POSetElement[Object]] */;
-/* Covariant cast for argument 0 (e) <p0:Object> isa E */
-/* <p0:Object> isa E */
-type_struct = self->type->resolution_table->types[COLOR_poset__POSet_FT0];
+val* var_poe /* var poe: POSetElement[nullable Object] */;
+val* var18 /* : HashSet[nullable Object] */;
+val* var20 /* : HashSet[nullable Object] */;
+val* var21 /* : HashSet[nullable Object] */;
+val* var23 /* : HashSet[nullable Object] */;
+val* var24 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+val* var26 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+/* Covariant cast for argument 0 (e) <p0:nullable Object> isa E */
+/* <p0:nullable Object> isa E */
+type_struct = self->type->resolution_table->types[COLOR_poset__POSet___35dE];
 cltype = type_struct->color;
 idtype = type_struct->id;
+is_nullable = type_struct->is_nullable;
+if(p0 == NULL) {
+var1 = is_nullable;
+} else {
 if(cltype >= p0->type->table_size) {
 var1 = 0;
 } else {
 var1 = p0->type->type_table[cltype] == idtype;
 }
+}
 if (unlikely(!var1)) {
 var_class_name = p0 == NULL ? "null" : p0->type->name;
 PRINT_ERROR("Runtime error: Cast failed. Expected `%s`, got `%s`", "E", var_class_name);
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 38);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 87);
 show_backtrace(1);
 }
 var_e = p0;
 {
-{ /* Inline poset#POSet#elements (self) on <self:POSet[Object]> */
-var4 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[Object]> */
+{ /* Inline poset#POSet#elements (self) on <self:POSet[nullable Object]> */
+var4 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[nullable Object]> */
 if (unlikely(var4 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _elements");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 33);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 82);
 show_backtrace(1);
 }
 var2 = var4;
@@ -211,11 +186,11 @@ RET_LABEL3:(void)0;
 }
 }
 {
-{ /* Inline hash_collection#HashMap#keys (var2) on <var2:HashMap[Object, POSetElement[Object]]> */
-var7 = var2->attrs[COLOR_hash_collection__HashMap___keys].val; /* _keys on <var2:HashMap[Object, POSetElement[Object]]> */
+{ /* Inline hash_collection#HashMap#keys (var2) on <var2:HashMap[nullable Object, POSetElement[nullable Object]]> */
+var7 = var2->attrs[COLOR_standard__hash_collection__HashMap___keys].val; /* _keys on <var2:HashMap[nullable Object, POSetElement[nullable Object]]> */
 if (unlikely(var7 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _keys");
-PRINT_ERROR(" (%s:%d)\n", "../lib/standard/collection/hash_collection.nit", 249);
+PRINT_ERROR(" (%s:%d)\n", FILE_standard__hash_collection, 275);
 show_backtrace(1);
 }
 var5 = var7;
@@ -223,15 +198,15 @@ RET_LABEL6:(void)0;
 }
 }
 {
-var8 = ((short int (*)(val*, val*))(var5->class->vft[COLOR_abstract_collection__Collection__has]))(var5, var_e) /* has on <var5:RemovableCollection[Object]>*/;
+var8 = ((short int (*)(val* self, val* p0))(var5->class->vft[COLOR_standard__abstract_collection__Collection__has]))(var5, var_e) /* has on <var5:RemovableCollection[nullable Object]>*/;
 }
 if (var8){
 {
-{ /* Inline poset#POSet#elements (self) on <self:POSet[Object]> */
-var11 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[Object]> */
+{ /* Inline poset#POSet#elements (self) on <self:POSet[nullable Object]> */
+var11 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[nullable Object]> */
 if (unlikely(var11 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _elements");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 33);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 82);
 show_backtrace(1);
 }
 var9 = var11;
@@ -239,19 +214,19 @@ RET_LABEL10:(void)0;
 }
 }
 {
-var12 = hash_collection__HashMap___91d_93d(var9, var_e);
+var12 = standard___standard__HashMap___standard__abstract_collection__MapRead___91d_93d(var9, var_e);
 }
 var = var12;
 goto RET_LABEL;
 } else {
 }
-var13 = NEW_poset__POSetElement(self->type->resolution_table->types[COLOR_poset__POSetElementposet__POSet_FT0]);
+var13 = NEW_poset__POSetElement(self->type->resolution_table->types[COLOR_poset__POSetElement__poset__POSet___35dE]);
 {
-{ /* Inline poset#POSet#elements (self) on <self:POSet[Object]> */
-var16 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[Object]> */
+{ /* Inline poset#POSet#elements (self) on <self:POSet[nullable Object]> */
+var16 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[nullable Object]> */
 if (unlikely(var16 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _elements");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 33);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 82);
 show_backtrace(1);
 }
 var14 = var16;
@@ -259,27 +234,27 @@ RET_LABEL15:(void)0;
 }
 }
 {
-var17 = hash_collection__HashMap__length(var14);
+var17 = standard___standard__HashMap___standard__abstract_collection__MapRead__length(var14);
 }
 {
-((void (*)(val*, val*))(var13->class->vft[COLOR_poset__POSetElement__poset_61d]))(var13, self) /* poset= on <var13:POSetElement[Object]>*/;
+((void (*)(val* self, val* p0))(var13->class->vft[COLOR_poset__POSetElement__poset_61d]))(var13, self) /* poset= on <var13:POSetElement[nullable Object]>*/;
 }
 {
-((void (*)(val*, val*))(var13->class->vft[COLOR_poset__POSetElement__element_61d]))(var13, var_e) /* element= on <var13:POSetElement[Object]>*/;
+((void (*)(val* self, val* p0))(var13->class->vft[COLOR_poset__POSetElement__element_61d]))(var13, var_e) /* element= on <var13:POSetElement[nullable Object]>*/;
 }
 {
-((void (*)(val*, long))(var13->class->vft[COLOR_poset__POSetElement__count_61d]))(var13, var17) /* count= on <var13:POSetElement[Object]>*/;
+((void (*)(val* self, long p0))(var13->class->vft[COLOR_poset__POSetElement__count_61d]))(var13, var17) /* count= on <var13:POSetElement[nullable Object]>*/;
 }
 {
-((void (*)(val*))(var13->class->vft[COLOR_kernel__Object__init]))(var13) /* init on <var13:POSetElement[Object]>*/;
+((void (*)(val* self))(var13->class->vft[COLOR_standard__kernel__Object__init]))(var13) /* init on <var13:POSetElement[nullable Object]>*/;
 }
 var_poe = var13;
 {
-{ /* Inline poset#POSetElement#tos (var_poe) on <var_poe:POSetElement[Object]> */
-var20 = var_poe->attrs[COLOR_poset__POSetElement___tos].val; /* _tos on <var_poe:POSetElement[Object]> */
+{ /* Inline poset#POSetElement#tos (var_poe) on <var_poe:POSetElement[nullable Object]> */
+var20 = var_poe->attrs[COLOR_poset__POSetElement___tos].val; /* _tos on <var_poe:POSetElement[nullable Object]> */
 if (unlikely(var20 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _tos");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 245);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 389);
 show_backtrace(1);
 }
 var18 = var20;
@@ -287,14 +262,14 @@ RET_LABEL19:(void)0;
 }
 }
 {
-hash_collection__HashSet__add(var18, var_e); /* Direct call hash_collection#HashSet#add on <var18:HashSet[Object]>*/
+standard___standard__HashSet___standard__abstract_collection__SimpleCollection__add(var18, var_e); /* Direct call hash_collection#HashSet#add on <var18:HashSet[nullable Object]>*/
 }
 {
-{ /* Inline poset#POSetElement#froms (var_poe) on <var_poe:POSetElement[Object]> */
-var23 = var_poe->attrs[COLOR_poset__POSetElement___froms].val; /* _froms on <var_poe:POSetElement[Object]> */
+{ /* Inline poset#POSetElement#froms (var_poe) on <var_poe:POSetElement[nullable Object]> */
+var23 = var_poe->attrs[COLOR_poset__POSetElement___froms].val; /* _froms on <var_poe:POSetElement[nullable Object]> */
 if (unlikely(var23 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _froms");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 246);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 390);
 show_backtrace(1);
 }
 var21 = var23;
@@ -302,14 +277,14 @@ RET_LABEL22:(void)0;
 }
 }
 {
-hash_collection__HashSet__add(var21, var_e); /* Direct call hash_collection#HashSet#add on <var21:HashSet[Object]>*/
+standard___standard__HashSet___standard__abstract_collection__SimpleCollection__add(var21, var_e); /* Direct call hash_collection#HashSet#add on <var21:HashSet[nullable Object]>*/
 }
 {
-{ /* Inline poset#POSet#elements (self) on <self:POSet[Object]> */
-var26 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[Object]> */
+{ /* Inline poset#POSet#elements (self) on <self:POSet[nullable Object]> */
+var26 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[nullable Object]> */
 if (unlikely(var26 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _elements");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 33);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 82);
 show_backtrace(1);
 }
 var24 = var26;
@@ -317,62 +292,59 @@ RET_LABEL25:(void)0;
 }
 }
 {
-hash_collection__HashMap___91d_93d_61d(var24, var_e, var_poe); /* Direct call hash_collection#HashMap#[]= on <var24:HashMap[Object, POSetElement[Object]]>*/
+standard___standard__HashMap___standard__abstract_collection__Map___91d_93d_61d(var24, var_e, var_poe); /* Direct call hash_collection#HashMap#[]= on <var24:HashMap[nullable Object, POSetElement[nullable Object]]>*/
 }
 var = var_poe;
 goto RET_LABEL;
 RET_LABEL:;
 return var;
 }
-/* method poset#POSet#add_node for (self: Object, Object): POSetElement[Object] */
-val* VIRTUAL_poset__POSet__add_node(val* self, val* p0) {
-val* var /* : POSetElement[Object] */;
-val* var1 /* : POSetElement[Object] */;
-var1 = poset__POSet__add_node(self, p0);
-var = var1;
-RET_LABEL:;
-return var;
-}
-/* method poset#POSet#[] for (self: POSet[Object], Object): POSetElement[Object] */
-val* poset__POSet___91d_93d(val* self, val* p0) {
-val* var /* : POSetElement[Object] */;
+/* method poset#POSet#[] for (self: POSet[nullable Object], nullable Object): POSetElement[nullable Object] */
+val* poset___poset__POSet____91d_93d(val* self, val* p0) {
+val* var /* : POSetElement[nullable Object] */;
 short int var1 /* : Bool */;
 int cltype;
 int idtype;
 const struct type* type_struct;
+short int is_nullable;
 const char* var_class_name;
-val* var_e /* var e: Object */;
-val* var2 /* : HashMap[Object, POSetElement[Object]] */;
-val* var4 /* : HashMap[Object, POSetElement[Object]] */;
-val* var5 /* : RemovableCollection[Object] */;
-val* var7 /* : RemovableCollection[Object] */;
+val* var_e /* var e: nullable Object */;
+val* var2 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+val* var4 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+val* var5 /* : RemovableCollection[nullable Object] */;
+val* var7 /* : RemovableCollection[nullable Object] */;
 short int var8 /* : Bool */;
-val* var9 /* : HashMap[Object, POSetElement[Object]] */;
-val* var11 /* : HashMap[Object, POSetElement[Object]] */;
+val* var9 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+val* var11 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
 val* var12 /* : nullable Object */;
-/* Covariant cast for argument 0 (e) <p0:Object> isa E */
-/* <p0:Object> isa E */
-type_struct = self->type->resolution_table->types[COLOR_poset__POSet_FT0];
+/* Covariant cast for argument 0 (e) <p0:nullable Object> isa E */
+/* <p0:nullable Object> isa E */
+type_struct = self->type->resolution_table->types[COLOR_poset__POSet___35dE];
 cltype = type_struct->color;
 idtype = type_struct->id;
+is_nullable = type_struct->is_nullable;
+if(p0 == NULL) {
+var1 = is_nullable;
+} else {
 if(cltype >= p0->type->table_size) {
 var1 = 0;
 } else {
 var1 = p0->type->type_table[cltype] == idtype;
 }
+}
 if (unlikely(!var1)) {
 var_class_name = p0 == NULL ? "null" : p0->type->name;
 PRINT_ERROR("Runtime error: Cast failed. Expected `%s`, got `%s`", "E", var_class_name);
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 52);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 101);
 show_backtrace(1);
 }
 var_e = p0;
 {
-{ /* Inline poset#POSet#elements (self) on <self:POSet[Object]> */
-var4 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[Object]> */
+{ /* Inline poset#POSet#elements (self) on <self:POSet[nullable Object]> */
+var4 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[nullable Object]> */
 if (unlikely(var4 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _elements");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 33);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 82);
 show_backtrace(1);
 }
 var2 = var4;
@@ -380,11 +352,11 @@ RET_LABEL3:(void)0;
 }
 }
 {
-{ /* Inline hash_collection#HashMap#keys (var2) on <var2:HashMap[Object, POSetElement[Object]]> */
-var7 = var2->attrs[COLOR_hash_collection__HashMap___keys].val; /* _keys on <var2:HashMap[Object, POSetElement[Object]]> */
+{ /* Inline hash_collection#HashMap#keys (var2) on <var2:HashMap[nullable Object, POSetElement[nullable Object]]> */
+var7 = var2->attrs[COLOR_standard__hash_collection__HashMap___keys].val; /* _keys on <var2:HashMap[nullable Object, POSetElement[nullable Object]]> */
 if (unlikely(var7 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _keys");
-PRINT_ERROR(" (%s:%d)\n", "../lib/standard/collection/hash_collection.nit", 249);
+PRINT_ERROR(" (%s:%d)\n", FILE_standard__hash_collection, 275);
 show_backtrace(1);
 }
 var5 = var7;
@@ -392,19 +364,19 @@ RET_LABEL6:(void)0;
 }
 }
 {
-var8 = ((short int (*)(val*, val*))(var5->class->vft[COLOR_abstract_collection__Collection__has]))(var5, var_e) /* has on <var5:RemovableCollection[Object]>*/;
+var8 = ((short int (*)(val* self, val* p0))(var5->class->vft[COLOR_standard__abstract_collection__Collection__has]))(var5, var_e) /* has on <var5:RemovableCollection[nullable Object]>*/;
 }
 if (unlikely(!var8)) {
 PRINT_ERROR("Runtime error: %s", "Assert failed");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 65);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 115);
 show_backtrace(1);
 }
 {
-{ /* Inline poset#POSet#elements (self) on <self:POSet[Object]> */
-var11 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[Object]> */
+{ /* Inline poset#POSet#elements (self) on <self:POSet[nullable Object]> */
+var11 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[nullable Object]> */
 if (unlikely(var11 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _elements");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 33);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 82);
 show_backtrace(1);
 }
 var9 = var11;
@@ -412,295 +384,298 @@ RET_LABEL10:(void)0;
 }
 }
 {
-var12 = hash_collection__HashMap___91d_93d(var9, var_e);
+var12 = standard___standard__HashMap___standard__abstract_collection__MapRead___91d_93d(var9, var_e);
 }
 var = var12;
 goto RET_LABEL;
 RET_LABEL:;
 return var;
 }
-/* method poset#POSet#[] for (self: Object, Object): POSetElement[Object] */
-val* VIRTUAL_poset__POSet___91d_93d(val* self, val* p0) {
-val* var /* : POSetElement[Object] */;
-val* var1 /* : POSetElement[Object] */;
-var1 = poset__POSet___91d_93d(self, p0);
-var = var1;
-RET_LABEL:;
-return var;
-}
-/* method poset#POSet#add_edge for (self: POSet[Object], Object, Object) */
-void poset__POSet__add_edge(val* self, val* p0, val* p1) {
+/* method poset#POSet#add_edge for (self: POSet[nullable Object], nullable Object, nullable Object) */
+void poset___poset__POSet___add_edge(val* self, val* p0, val* p1) {
 short int var /* : Bool */;
 int cltype;
 int idtype;
 const struct type* type_struct;
+short int is_nullable;
 const char* var_class_name;
 short int var1 /* : Bool */;
 int cltype2;
 int idtype3;
 const struct type* type_struct4;
-const char* var_class_name5;
-val* var_f /* var f: Object */;
-val* var_t /* var t: Object */;
-val* var6 /* : POSetElement[Object] */;
-val* var_fe /* var fe: POSetElement[Object] */;
-val* var7 /* : POSetElement[Object] */;
-val* var_te /* var te: POSetElement[Object] */;
-val* var8 /* : HashSet[Object] */;
-val* var10 /* : HashSet[Object] */;
-short int var11 /* : Bool */;
-val* var12 /* : HashSet[Object] */;
-val* var14 /* : HashSet[Object] */;
-val* var_ /* var : HashSet[Object] */;
-val* var15 /* : Iterator[Object] */;
-val* var_16 /* var : Iterator[Object] */;
-short int var17 /* : Bool */;
-val* var18 /* : nullable Object */;
-val* var_ff /* var ff: Object */;
-val* var19 /* : HashMap[Object, POSetElement[Object]] */;
-val* var21 /* : HashMap[Object, POSetElement[Object]] */;
-val* var22 /* : nullable Object */;
-val* var_ffe /* var ffe: POSetElement[Object] */;
-val* var23 /* : HashSet[Object] */;
-val* var25 /* : HashSet[Object] */;
-val* var_26 /* var : HashSet[Object] */;
-val* var27 /* : Iterator[Object] */;
-val* var_28 /* var : Iterator[Object] */;
-short int var29 /* : Bool */;
-val* var30 /* : nullable Object */;
-val* var_tt /* var tt: Object */;
-val* var31 /* : HashMap[Object, POSetElement[Object]] */;
-val* var33 /* : HashMap[Object, POSetElement[Object]] */;
-val* var34 /* : nullable Object */;
-val* var_tte /* var tte: POSetElement[Object] */;
-val* var35 /* : HashSet[Object] */;
-val* var37 /* : HashSet[Object] */;
-val* var38 /* : HashSet[Object] */;
-val* var40 /* : HashSet[Object] */;
-val* var44 /* : HashSet[Object] */;
-val* var46 /* : HashSet[Object] */;
-short int var47 /* : Bool */;
-val* var48 /* : HashSet[Object] */;
-val* var50 /* : HashSet[Object] */;
-val* var51 /* : Array[nullable Object] */;
-val* var_52 /* var : Array[Object] */;
-val* var53 /* : ArrayIterator[nullable Object] */;
-val* var_54 /* var : ArrayIterator[Object] */;
-short int var55 /* : Bool */;
-val* var56 /* : nullable Object */;
-val* var_x /* var x: Object */;
-val* var57 /* : HashMap[Object, POSetElement[Object]] */;
-val* var59 /* : HashMap[Object, POSetElement[Object]] */;
-val* var60 /* : nullable Object */;
-val* var_xe /* var xe: POSetElement[Object] */;
-val* var61 /* : HashSet[Object] */;
-val* var63 /* : HashSet[Object] */;
-short int var64 /* : Bool */;
-val* var65 /* : HashSet[Object] */;
-val* var67 /* : HashSet[Object] */;
-val* var68 /* : HashSet[Object] */;
-val* var70 /* : HashSet[Object] */;
-val* var73 /* : HashSet[Object] */;
-val* var75 /* : HashSet[Object] */;
-val* var76 /* : Array[nullable Object] */;
-val* var_77 /* var : Array[Object] */;
-val* var78 /* : ArrayIterator[nullable Object] */;
-val* var_79 /* var : ArrayIterator[Object] */;
-short int var80 /* : Bool */;
-val* var81 /* : nullable Object */;
-val* var_x82 /* var x: Object */;
-val* var83 /* : HashMap[Object, POSetElement[Object]] */;
-val* var85 /* : HashMap[Object, POSetElement[Object]] */;
-val* var86 /* : nullable Object */;
-val* var_xe87 /* var xe: POSetElement[Object] */;
-val* var88 /* : HashSet[Object] */;
-val* var90 /* : HashSet[Object] */;
-short int var91 /* : Bool */;
-val* var92 /* : HashSet[Object] */;
-val* var94 /* : HashSet[Object] */;
-val* var95 /* : HashSet[Object] */;
-val* var97 /* : HashSet[Object] */;
-val* var100 /* : HashSet[Object] */;
-val* var102 /* : HashSet[Object] */;
-val* var103 /* : HashSet[Object] */;
-val* var105 /* : HashSet[Object] */;
-/* Covariant cast for argument 0 (f) <p0:Object> isa E */
-/* <p0:Object> isa E */
-type_struct = self->type->resolution_table->types[COLOR_poset__POSet_FT0];
+short int is_nullable5;
+const char* var_class_name6;
+val* var_f /* var f: nullable Object */;
+val* var_t /* var t: nullable Object */;
+val* var7 /* : POSetElement[nullable Object] */;
+val* var_fe /* var fe: POSetElement[nullable Object] */;
+val* var8 /* : POSetElement[nullable Object] */;
+val* var_te /* var te: POSetElement[nullable Object] */;
+val* var9 /* : HashSet[nullable Object] */;
+val* var11 /* : HashSet[nullable Object] */;
+short int var12 /* : Bool */;
+val* var13 /* : HashSet[nullable Object] */;
+val* var15 /* : HashSet[nullable Object] */;
+val* var_ /* var : HashSet[nullable Object] */;
+val* var16 /* : Iterator[nullable Object] */;
+val* var_17 /* var : Iterator[nullable Object] */;
+short int var18 /* : Bool */;
+val* var19 /* : nullable Object */;
+val* var_ff /* var ff: nullable Object */;
+val* var20 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+val* var22 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+val* var23 /* : nullable Object */;
+val* var_ffe /* var ffe: POSetElement[nullable Object] */;
+val* var24 /* : HashSet[nullable Object] */;
+val* var26 /* : HashSet[nullable Object] */;
+val* var_27 /* var : HashSet[nullable Object] */;
+val* var28 /* : Iterator[nullable Object] */;
+val* var_29 /* var : Iterator[nullable Object] */;
+short int var30 /* : Bool */;
+val* var31 /* : nullable Object */;
+val* var_tt /* var tt: nullable Object */;
+val* var32 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+val* var34 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+val* var35 /* : nullable Object */;
+val* var_tte /* var tte: POSetElement[nullable Object] */;
+val* var36 /* : HashSet[nullable Object] */;
+val* var38 /* : HashSet[nullable Object] */;
+val* var39 /* : HashSet[nullable Object] */;
+val* var41 /* : HashSet[nullable Object] */;
+val* var45 /* : HashSet[nullable Object] */;
+val* var47 /* : HashSet[nullable Object] */;
+short int var48 /* : Bool */;
+val* var49 /* : HashSet[nullable Object] */;
+val* var51 /* : HashSet[nullable Object] */;
+val* var52 /* : Array[nullable Object] */;
+val* var_53 /* var : Array[nullable Object] */;
+val* var54 /* : ArrayIterator[nullable Object] */;
+val* var_55 /* var : ArrayIterator[nullable Object] */;
+short int var56 /* : Bool */;
+val* var57 /* : nullable Object */;
+val* var_x /* var x: nullable Object */;
+val* var58 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+val* var60 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+val* var61 /* : nullable Object */;
+val* var_xe /* var xe: POSetElement[nullable Object] */;
+val* var62 /* : HashSet[nullable Object] */;
+val* var64 /* : HashSet[nullable Object] */;
+short int var65 /* : Bool */;
+val* var66 /* : HashSet[nullable Object] */;
+val* var68 /* : HashSet[nullable Object] */;
+val* var69 /* : HashSet[nullable Object] */;
+val* var71 /* : HashSet[nullable Object] */;
+val* var74 /* : HashSet[nullable Object] */;
+val* var76 /* : HashSet[nullable Object] */;
+val* var77 /* : Array[nullable Object] */;
+val* var_78 /* var : Array[nullable Object] */;
+val* var79 /* : ArrayIterator[nullable Object] */;
+val* var_80 /* var : ArrayIterator[nullable Object] */;
+short int var81 /* : Bool */;
+val* var82 /* : nullable Object */;
+val* var_x83 /* var x: nullable Object */;
+val* var84 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+val* var86 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+val* var87 /* : nullable Object */;
+val* var_xe88 /* var xe: POSetElement[nullable Object] */;
+val* var89 /* : HashSet[nullable Object] */;
+val* var91 /* : HashSet[nullable Object] */;
+short int var92 /* : Bool */;
+val* var93 /* : HashSet[nullable Object] */;
+val* var95 /* : HashSet[nullable Object] */;
+val* var96 /* : HashSet[nullable Object] */;
+val* var98 /* : HashSet[nullable Object] */;
+val* var101 /* : HashSet[nullable Object] */;
+val* var103 /* : HashSet[nullable Object] */;
+val* var104 /* : HashSet[nullable Object] */;
+val* var106 /* : HashSet[nullable Object] */;
+/* Covariant cast for argument 0 (f) <p0:nullable Object> isa E */
+/* <p0:nullable Object> isa E */
+type_struct = self->type->resolution_table->types[COLOR_poset__POSet___35dE];
 cltype = type_struct->color;
 idtype = type_struct->id;
+is_nullable = type_struct->is_nullable;
+if(p0 == NULL) {
+var = is_nullable;
+} else {
 if(cltype >= p0->type->table_size) {
 var = 0;
 } else {
 var = p0->type->type_table[cltype] == idtype;
 }
+}
 if (unlikely(!var)) {
 var_class_name = p0 == NULL ? "null" : p0->type->name;
 PRINT_ERROR("Runtime error: Cast failed. Expected `%s`, got `%s`", "E", var_class_name);
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 69);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 119);
 show_backtrace(1);
 }
-/* Covariant cast for argument 1 (t) <p1:Object> isa E */
-/* <p1:Object> isa E */
-type_struct4 = self->type->resolution_table->types[COLOR_poset__POSet_FT0];
+/* Covariant cast for argument 1 (t) <p1:nullable Object> isa E */
+/* <p1:nullable Object> isa E */
+type_struct4 = self->type->resolution_table->types[COLOR_poset__POSet___35dE];
 cltype2 = type_struct4->color;
 idtype3 = type_struct4->id;
+is_nullable5 = type_struct4->is_nullable;
+if(p1 == NULL) {
+var1 = is_nullable5;
+} else {
 if(cltype2 >= p1->type->table_size) {
 var1 = 0;
 } else {
 var1 = p1->type->type_table[cltype2] == idtype3;
 }
+}
 if (unlikely(!var1)) {
-var_class_name5 = p1 == NULL ? "null" : p1->type->name;
-PRINT_ERROR("Runtime error: Cast failed. Expected `%s`, got `%s`", "E", var_class_name5);
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 69);
+var_class_name6 = p1 == NULL ? "null" : p1->type->name;
+PRINT_ERROR("Runtime error: Cast failed. Expected `%s`, got `%s`", "E", var_class_name6);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 119);
 show_backtrace(1);
 }
 var_f = p0;
 var_t = p1;
 {
-var6 = poset__POSet__add_node(self, var_f);
+var7 = poset___poset__POSet___add_node(self, var_f);
 }
-var_fe = var6;
+var_fe = var7;
 {
-var7 = poset__POSet__add_node(self, var_t);
+var8 = poset___poset__POSet___add_node(self, var_t);
 }
-var_te = var7;
+var_te = var8;
 {
-{ /* Inline poset#POSetElement#tos (var_fe) on <var_fe:POSetElement[Object]> */
-var10 = var_fe->attrs[COLOR_poset__POSetElement___tos].val; /* _tos on <var_fe:POSetElement[Object]> */
-if (unlikely(var10 == NULL)) {
+{ /* Inline poset#POSetElement#tos (var_fe) on <var_fe:POSetElement[nullable Object]> */
+var11 = var_fe->attrs[COLOR_poset__POSetElement___tos].val; /* _tos on <var_fe:POSetElement[nullable Object]> */
+if (unlikely(var11 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _tos");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 245);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 389);
 show_backtrace(1);
 }
-var8 = var10;
-RET_LABEL9:(void)0;
+var9 = var11;
+RET_LABEL10:(void)0;
 }
 }
 {
-var11 = hash_collection__HashSet__has(var8, var_t);
+var12 = standard___standard__HashSet___standard__abstract_collection__Collection__has(var9, var_t);
 }
-if (var11){
+if (var12){
 goto RET_LABEL;
 } else {
 }
 {
-{ /* Inline poset#POSetElement#froms (var_fe) on <var_fe:POSetElement[Object]> */
-var14 = var_fe->attrs[COLOR_poset__POSetElement___froms].val; /* _froms on <var_fe:POSetElement[Object]> */
-if (unlikely(var14 == NULL)) {
+{ /* Inline poset#POSetElement#froms (var_fe) on <var_fe:POSetElement[nullable Object]> */
+var15 = var_fe->attrs[COLOR_poset__POSetElement___froms].val; /* _froms on <var_fe:POSetElement[nullable Object]> */
+if (unlikely(var15 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _froms");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 246);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 390);
 show_backtrace(1);
 }
-var12 = var14;
-RET_LABEL13:(void)0;
+var13 = var15;
+RET_LABEL14:(void)0;
 }
 }
-var_ = var12;
+var_ = var13;
 {
-var15 = hash_collection__HashSet__iterator(var_);
+var16 = standard___standard__HashSet___standard__abstract_collection__Collection__iterator(var_);
 }
-var_16 = var15;
+var_17 = var16;
 for(;;) {
 {
-var17 = ((short int (*)(val*))(var_16->class->vft[COLOR_abstract_collection__Iterator__is_ok]))(var_16) /* is_ok on <var_16:Iterator[Object]>*/;
+var18 = ((short int (*)(val* self))(var_17->class->vft[COLOR_standard__abstract_collection__Iterator__is_ok]))(var_17) /* is_ok on <var_17:Iterator[nullable Object]>*/;
 }
-if (var17){
+if (var18){
 {
-var18 = ((val* (*)(val*))(var_16->class->vft[COLOR_abstract_collection__Iterator__item]))(var_16) /* item on <var_16:Iterator[Object]>*/;
+var19 = ((val* (*)(val* self))(var_17->class->vft[COLOR_standard__abstract_collection__Iterator__item]))(var_17) /* item on <var_17:Iterator[nullable Object]>*/;
 }
-var_ff = var18;
+var_ff = var19;
 {
-{ /* Inline poset#POSet#elements (self) on <self:POSet[Object]> */
-var21 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[Object]> */
-if (unlikely(var21 == NULL)) {
+{ /* Inline poset#POSet#elements (self) on <self:POSet[nullable Object]> */
+var22 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[nullable Object]> */
+if (unlikely(var22 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _elements");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 33);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 82);
 show_backtrace(1);
 }
-var19 = var21;
-RET_LABEL20:(void)0;
+var20 = var22;
+RET_LABEL21:(void)0;
 }
 }
 {
-var22 = hash_collection__HashMap___91d_93d(var19, var_ff);
+var23 = standard___standard__HashMap___standard__abstract_collection__MapRead___91d_93d(var20, var_ff);
 }
-var_ffe = var22;
+var_ffe = var23;
 {
-{ /* Inline poset#POSetElement#tos (var_te) on <var_te:POSetElement[Object]> */
-var25 = var_te->attrs[COLOR_poset__POSetElement___tos].val; /* _tos on <var_te:POSetElement[Object]> */
-if (unlikely(var25 == NULL)) {
+{ /* Inline poset#POSetElement#tos (var_te) on <var_te:POSetElement[nullable Object]> */
+var26 = var_te->attrs[COLOR_poset__POSetElement___tos].val; /* _tos on <var_te:POSetElement[nullable Object]> */
+if (unlikely(var26 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _tos");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 245);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 389);
 show_backtrace(1);
 }
-var23 = var25;
-RET_LABEL24:(void)0;
+var24 = var26;
+RET_LABEL25:(void)0;
 }
 }
-var_26 = var23;
+var_27 = var24;
 {
-var27 = hash_collection__HashSet__iterator(var_26);
+var28 = standard___standard__HashSet___standard__abstract_collection__Collection__iterator(var_27);
 }
-var_28 = var27;
+var_29 = var28;
 for(;;) {
 {
-var29 = ((short int (*)(val*))(var_28->class->vft[COLOR_abstract_collection__Iterator__is_ok]))(var_28) /* is_ok on <var_28:Iterator[Object]>*/;
+var30 = ((short int (*)(val* self))(var_29->class->vft[COLOR_standard__abstract_collection__Iterator__is_ok]))(var_29) /* is_ok on <var_29:Iterator[nullable Object]>*/;
 }
-if (var29){
+if (var30){
 {
-var30 = ((val* (*)(val*))(var_28->class->vft[COLOR_abstract_collection__Iterator__item]))(var_28) /* item on <var_28:Iterator[Object]>*/;
+var31 = ((val* (*)(val* self))(var_29->class->vft[COLOR_standard__abstract_collection__Iterator__item]))(var_29) /* item on <var_29:Iterator[nullable Object]>*/;
 }
-var_tt = var30;
+var_tt = var31;
 {
-{ /* Inline poset#POSet#elements (self) on <self:POSet[Object]> */
-var33 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[Object]> */
-if (unlikely(var33 == NULL)) {
+{ /* Inline poset#POSet#elements (self) on <self:POSet[nullable Object]> */
+var34 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[nullable Object]> */
+if (unlikely(var34 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _elements");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 33);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 82);
 show_backtrace(1);
 }
-var31 = var33;
-RET_LABEL32:(void)0;
+var32 = var34;
+RET_LABEL33:(void)0;
 }
 }
 {
-var34 = hash_collection__HashMap___91d_93d(var31, var_tt);
+var35 = standard___standard__HashMap___standard__abstract_collection__MapRead___91d_93d(var32, var_tt);
 }
-var_tte = var34;
+var_tte = var35;
 {
-{ /* Inline poset#POSetElement#froms (var_tte) on <var_tte:POSetElement[Object]> */
-var37 = var_tte->attrs[COLOR_poset__POSetElement___froms].val; /* _froms on <var_tte:POSetElement[Object]> */
-if (unlikely(var37 == NULL)) {
+{ /* Inline poset#POSetElement#froms (var_tte) on <var_tte:POSetElement[nullable Object]> */
+var38 = var_tte->attrs[COLOR_poset__POSetElement___froms].val; /* _froms on <var_tte:POSetElement[nullable Object]> */
+if (unlikely(var38 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _froms");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 246);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 390);
 show_backtrace(1);
 }
-var35 = var37;
-RET_LABEL36:(void)0;
+var36 = var38;
+RET_LABEL37:(void)0;
 }
 }
 {
-hash_collection__HashSet__add(var35, var_ff); /* Direct call hash_collection#HashSet#add on <var35:HashSet[Object]>*/
+standard___standard__HashSet___standard__abstract_collection__SimpleCollection__add(var36, var_ff); /* Direct call hash_collection#HashSet#add on <var36:HashSet[nullable Object]>*/
 }
 {
-{ /* Inline poset#POSetElement#tos (var_ffe) on <var_ffe:POSetElement[Object]> */
-var40 = var_ffe->attrs[COLOR_poset__POSetElement___tos].val; /* _tos on <var_ffe:POSetElement[Object]> */
-if (unlikely(var40 == NULL)) {
+{ /* Inline poset#POSetElement#tos (var_ffe) on <var_ffe:POSetElement[nullable Object]> */
+var41 = var_ffe->attrs[COLOR_poset__POSetElement___tos].val; /* _tos on <var_ffe:POSetElement[nullable Object]> */
+if (unlikely(var41 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _tos");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 245);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 389);
 show_backtrace(1);
 }
-var38 = var40;
-RET_LABEL39:(void)0;
+var39 = var41;
+RET_LABEL40:(void)0;
 }
 }
 {
-hash_collection__HashSet__add(var38, var_tt); /* Direct call hash_collection#HashSet#add on <var38:HashSet[Object]>*/
+standard___standard__HashSet___standard__abstract_collection__SimpleCollection__add(var39, var_tt); /* Direct call hash_collection#HashSet#add on <var39:HashSet[nullable Object]>*/
 }
 {
-((void (*)(val*))(var_28->class->vft[COLOR_abstract_collection__Iterator__next]))(var_28) /* next on <var_28:Iterator[Object]>*/;
+((void (*)(val* self))(var_29->class->vft[COLOR_standard__abstract_collection__Iterator__next]))(var_29) /* next on <var_29:Iterator[nullable Object]>*/;
 }
 } else {
 goto BREAK_label;
@@ -708,460 +683,465 @@ goto BREAK_label;
 }
 BREAK_label: (void)0;
 {
-{ /* Inline abstract_collection#Iterator#finish (var_28) on <var_28:Iterator[Object]> */
-RET_LABEL41:(void)0;
+{ /* Inline abstract_collection#Iterator#finish (var_29) on <var_29:Iterator[nullable Object]> */
+RET_LABEL42:(void)0;
 }
 }
 {
-((void (*)(val*))(var_16->class->vft[COLOR_abstract_collection__Iterator__next]))(var_16) /* next on <var_16:Iterator[Object]>*/;
+((void (*)(val* self))(var_17->class->vft[COLOR_standard__abstract_collection__Iterator__next]))(var_17) /* next on <var_17:Iterator[nullable Object]>*/;
 }
 } else {
-goto BREAK_label42;
+goto BREAK_label43;
 }
 }
-BREAK_label42: (void)0;
+BREAK_label43: (void)0;
 {
-{ /* Inline abstract_collection#Iterator#finish (var_16) on <var_16:Iterator[Object]> */
-RET_LABEL43:(void)0;
+{ /* Inline abstract_collection#Iterator#finish (var_17) on <var_17:Iterator[nullable Object]> */
+RET_LABEL44:(void)0;
 }
 }
 {
-{ /* Inline poset#POSetElement#tos (var_te) on <var_te:POSetElement[Object]> */
-var46 = var_te->attrs[COLOR_poset__POSetElement___tos].val; /* _tos on <var_te:POSetElement[Object]> */
-if (unlikely(var46 == NULL)) {
+{ /* Inline poset#POSetElement#tos (var_te) on <var_te:POSetElement[nullable Object]> */
+var47 = var_te->attrs[COLOR_poset__POSetElement___tos].val; /* _tos on <var_te:POSetElement[nullable Object]> */
+if (unlikely(var47 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _tos");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 245);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 389);
 show_backtrace(1);
 }
-var44 = var46;
-RET_LABEL45:(void)0;
+var45 = var47;
+RET_LABEL46:(void)0;
 }
 }
 {
-var47 = hash_collection__HashSet__has(var44, var_f);
+var48 = standard___standard__HashSet___standard__abstract_collection__Collection__has(var45, var_f);
 }
-if (var47){
+if (var48){
 goto RET_LABEL;
 } else {
 }
 {
-{ /* Inline poset#POSetElement#dfroms (var_te) on <var_te:POSetElement[Object]> */
-var50 = var_te->attrs[COLOR_poset__POSetElement___dfroms].val; /* _dfroms on <var_te:POSetElement[Object]> */
-if (unlikely(var50 == NULL)) {
+{ /* Inline poset#POSetElement#dfroms (var_te) on <var_te:POSetElement[nullable Object]> */
+var51 = var_te->attrs[COLOR_poset__POSetElement___dfroms].val; /* _dfroms on <var_te:POSetElement[nullable Object]> */
+if (unlikely(var51 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _dfroms");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 248);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 392);
 show_backtrace(1);
 }
-var48 = var50;
-RET_LABEL49:(void)0;
+var49 = var51;
+RET_LABEL50:(void)0;
 }
 }
 {
-var51 = array__Collection__to_a(var48);
+var52 = standard__array___Collection___to_a(var49);
 }
-var_52 = var51;
+var_53 = var52;
 {
-var53 = array__AbstractArrayRead__iterator(var_52);
+var54 = standard___standard__AbstractArrayRead___standard__abstract_collection__Collection__iterator(var_53);
 }
-var_54 = var53;
+var_55 = var54;
 for(;;) {
 {
-var55 = array__ArrayIterator__is_ok(var_54);
+var56 = standard__array___standard__array__ArrayIterator___standard__abstract_collection__Iterator__is_ok(var_55);
 }
-if (var55){
+if (var56){
 {
-var56 = array__ArrayIterator__item(var_54);
+var57 = standard__array___standard__array__ArrayIterator___standard__abstract_collection__Iterator__item(var_55);
 }
-var_x = var56;
+var_x = var57;
 {
-{ /* Inline poset#POSet#elements (self) on <self:POSet[Object]> */
-var59 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[Object]> */
-if (unlikely(var59 == NULL)) {
+{ /* Inline poset#POSet#elements (self) on <self:POSet[nullable Object]> */
+var60 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[nullable Object]> */
+if (unlikely(var60 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _elements");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 33);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 82);
 show_backtrace(1);
 }
-var57 = var59;
-RET_LABEL58:(void)0;
+var58 = var60;
+RET_LABEL59:(void)0;
 }
 }
 {
-var60 = hash_collection__HashMap___91d_93d(var57, var_x);
+var61 = standard___standard__HashMap___standard__abstract_collection__MapRead___91d_93d(var58, var_x);
 }
-var_xe = var60;
+var_xe = var61;
 {
-{ /* Inline poset#POSetElement#tos (var_xe) on <var_xe:POSetElement[Object]> */
-var63 = var_xe->attrs[COLOR_poset__POSetElement___tos].val; /* _tos on <var_xe:POSetElement[Object]> */
-if (unlikely(var63 == NULL)) {
+{ /* Inline poset#POSetElement#tos (var_xe) on <var_xe:POSetElement[nullable Object]> */
+var64 = var_xe->attrs[COLOR_poset__POSetElement___tos].val; /* _tos on <var_xe:POSetElement[nullable Object]> */
+if (unlikely(var64 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _tos");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 245);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 389);
 show_backtrace(1);
 }
-var61 = var63;
-RET_LABEL62:(void)0;
+var62 = var64;
+RET_LABEL63:(void)0;
 }
 }
 {
-var64 = hash_collection__HashSet__has(var61, var_f);
+var65 = standard___standard__HashSet___standard__abstract_collection__Collection__has(var62, var_f);
 }
-if (var64){
+if (var65){
 {
-{ /* Inline poset#POSetElement#dfroms (var_te) on <var_te:POSetElement[Object]> */
-var67 = var_te->attrs[COLOR_poset__POSetElement___dfroms].val; /* _dfroms on <var_te:POSetElement[Object]> */
-if (unlikely(var67 == NULL)) {
+{ /* Inline poset#POSetElement#dfroms (var_te) on <var_te:POSetElement[nullable Object]> */
+var68 = var_te->attrs[COLOR_poset__POSetElement___dfroms].val; /* _dfroms on <var_te:POSetElement[nullable Object]> */
+if (unlikely(var68 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _dfroms");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 248);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 392);
 show_backtrace(1);
 }
-var65 = var67;
-RET_LABEL66:(void)0;
+var66 = var68;
+RET_LABEL67:(void)0;
 }
 }
 {
-hash_collection__HashSet__remove(var65, var_x); /* Direct call hash_collection#HashSet#remove on <var65:HashSet[Object]>*/
+standard___standard__HashSet___standard__abstract_collection__RemovableCollection__remove(var66, var_x); /* Direct call hash_collection#HashSet#remove on <var66:HashSet[nullable Object]>*/
 }
 {
-{ /* Inline poset#POSetElement#dtos (var_xe) on <var_xe:POSetElement[Object]> */
-var70 = var_xe->attrs[COLOR_poset__POSetElement___dtos].val; /* _dtos on <var_xe:POSetElement[Object]> */
-if (unlikely(var70 == NULL)) {
+{ /* Inline poset#POSetElement#dtos (var_xe) on <var_xe:POSetElement[nullable Object]> */
+var71 = var_xe->attrs[COLOR_poset__POSetElement___dtos].val; /* _dtos on <var_xe:POSetElement[nullable Object]> */
+if (unlikely(var71 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _dtos");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 247);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 391);
 show_backtrace(1);
 }
-var68 = var70;
-RET_LABEL69:(void)0;
+var69 = var71;
+RET_LABEL70:(void)0;
 }
 }
 {
-hash_collection__HashSet__remove(var68, var_t); /* Direct call hash_collection#HashSet#remove on <var68:HashSet[Object]>*/
+standard___standard__HashSet___standard__abstract_collection__RemovableCollection__remove(var69, var_t); /* Direct call hash_collection#HashSet#remove on <var69:HashSet[nullable Object]>*/
 }
 } else {
 }
 {
-array__ArrayIterator__next(var_54); /* Direct call array#ArrayIterator#next on <var_54:ArrayIterator[Object]>*/
+standard__array___standard__array__ArrayIterator___standard__abstract_collection__Iterator__next(var_55); /* Direct call array#ArrayIterator#next on <var_55:ArrayIterator[nullable Object]>*/
 }
 } else {
-goto BREAK_label71;
+goto BREAK_label72;
 }
 }
-BREAK_label71: (void)0;
+BREAK_label72: (void)0;
 {
-{ /* Inline abstract_collection#Iterator#finish (var_54) on <var_54:ArrayIterator[Object]> */
-RET_LABEL72:(void)0;
+{ /* Inline abstract_collection#Iterator#finish (var_55) on <var_55:ArrayIterator[nullable Object]> */
+RET_LABEL73:(void)0;
 }
 }
 {
-{ /* Inline poset#POSetElement#dtos (var_fe) on <var_fe:POSetElement[Object]> */
-var75 = var_fe->attrs[COLOR_poset__POSetElement___dtos].val; /* _dtos on <var_fe:POSetElement[Object]> */
-if (unlikely(var75 == NULL)) {
+{ /* Inline poset#POSetElement#dtos (var_fe) on <var_fe:POSetElement[nullable Object]> */
+var76 = var_fe->attrs[COLOR_poset__POSetElement___dtos].val; /* _dtos on <var_fe:POSetElement[nullable Object]> */
+if (unlikely(var76 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _dtos");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 247);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 391);
 show_backtrace(1);
 }
-var73 = var75;
-RET_LABEL74:(void)0;
+var74 = var76;
+RET_LABEL75:(void)0;
 }
 }
 {
-var76 = array__Collection__to_a(var73);
+var77 = standard__array___Collection___to_a(var74);
 }
-var_77 = var76;
+var_78 = var77;
 {
-var78 = array__AbstractArrayRead__iterator(var_77);
+var79 = standard___standard__AbstractArrayRead___standard__abstract_collection__Collection__iterator(var_78);
 }
-var_79 = var78;
+var_80 = var79;
 for(;;) {
 {
-var80 = array__ArrayIterator__is_ok(var_79);
+var81 = standard__array___standard__array__ArrayIterator___standard__abstract_collection__Iterator__is_ok(var_80);
 }
-if (var80){
+if (var81){
 {
-var81 = array__ArrayIterator__item(var_79);
+var82 = standard__array___standard__array__ArrayIterator___standard__abstract_collection__Iterator__item(var_80);
 }
-var_x82 = var81;
+var_x83 = var82;
 {
-{ /* Inline poset#POSet#elements (self) on <self:POSet[Object]> */
-var85 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[Object]> */
-if (unlikely(var85 == NULL)) {
+{ /* Inline poset#POSet#elements (self) on <self:POSet[nullable Object]> */
+var86 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[nullable Object]> */
+if (unlikely(var86 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _elements");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 33);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 82);
 show_backtrace(1);
 }
-var83 = var85;
-RET_LABEL84:(void)0;
+var84 = var86;
+RET_LABEL85:(void)0;
 }
 }
 {
-var86 = hash_collection__HashMap___91d_93d(var83, var_x82);
+var87 = standard___standard__HashMap___standard__abstract_collection__MapRead___91d_93d(var84, var_x83);
 }
-var_xe87 = var86;
+var_xe88 = var87;
 {
-{ /* Inline poset#POSetElement#froms (var_xe87) on <var_xe87:POSetElement[Object]> */
-var90 = var_xe87->attrs[COLOR_poset__POSetElement___froms].val; /* _froms on <var_xe87:POSetElement[Object]> */
-if (unlikely(var90 == NULL)) {
+{ /* Inline poset#POSetElement#froms (var_xe88) on <var_xe88:POSetElement[nullable Object]> */
+var91 = var_xe88->attrs[COLOR_poset__POSetElement___froms].val; /* _froms on <var_xe88:POSetElement[nullable Object]> */
+if (unlikely(var91 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _froms");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 246);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 390);
 show_backtrace(1);
 }
-var88 = var90;
-RET_LABEL89:(void)0;
+var89 = var91;
+RET_LABEL90:(void)0;
 }
 }
 {
-var91 = hash_collection__HashSet__has(var88, var_t);
+var92 = standard___standard__HashSet___standard__abstract_collection__Collection__has(var89, var_t);
 }
-if (var91){
+if (var92){
 {
-{ /* Inline poset#POSetElement#dfroms (var_xe87) on <var_xe87:POSetElement[Object]> */
-var94 = var_xe87->attrs[COLOR_poset__POSetElement___dfroms].val; /* _dfroms on <var_xe87:POSetElement[Object]> */
-if (unlikely(var94 == NULL)) {
+{ /* Inline poset#POSetElement#dfroms (var_xe88) on <var_xe88:POSetElement[nullable Object]> */
+var95 = var_xe88->attrs[COLOR_poset__POSetElement___dfroms].val; /* _dfroms on <var_xe88:POSetElement[nullable Object]> */
+if (unlikely(var95 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _dfroms");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 248);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 392);
 show_backtrace(1);
 }
-var92 = var94;
-RET_LABEL93:(void)0;
+var93 = var95;
+RET_LABEL94:(void)0;
 }
 }
 {
-hash_collection__HashSet__remove(var92, var_f); /* Direct call hash_collection#HashSet#remove on <var92:HashSet[Object]>*/
+standard___standard__HashSet___standard__abstract_collection__RemovableCollection__remove(var93, var_f); /* Direct call hash_collection#HashSet#remove on <var93:HashSet[nullable Object]>*/
 }
 {
-{ /* Inline poset#POSetElement#dtos (var_fe) on <var_fe:POSetElement[Object]> */
-var97 = var_fe->attrs[COLOR_poset__POSetElement___dtos].val; /* _dtos on <var_fe:POSetElement[Object]> */
-if (unlikely(var97 == NULL)) {
+{ /* Inline poset#POSetElement#dtos (var_fe) on <var_fe:POSetElement[nullable Object]> */
+var98 = var_fe->attrs[COLOR_poset__POSetElement___dtos].val; /* _dtos on <var_fe:POSetElement[nullable Object]> */
+if (unlikely(var98 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _dtos");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 247);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 391);
 show_backtrace(1);
 }
-var95 = var97;
-RET_LABEL96:(void)0;
+var96 = var98;
+RET_LABEL97:(void)0;
 }
 }
 {
-hash_collection__HashSet__remove(var95, var_x82); /* Direct call hash_collection#HashSet#remove on <var95:HashSet[Object]>*/
+standard___standard__HashSet___standard__abstract_collection__RemovableCollection__remove(var96, var_x83); /* Direct call hash_collection#HashSet#remove on <var96:HashSet[nullable Object]>*/
 }
 } else {
 }
 {
-array__ArrayIterator__next(var_79); /* Direct call array#ArrayIterator#next on <var_79:ArrayIterator[Object]>*/
+standard__array___standard__array__ArrayIterator___standard__abstract_collection__Iterator__next(var_80); /* Direct call array#ArrayIterator#next on <var_80:ArrayIterator[nullable Object]>*/
 }
 } else {
-goto BREAK_label98;
+goto BREAK_label99;
 }
 }
-BREAK_label98: (void)0;
+BREAK_label99: (void)0;
 {
-{ /* Inline abstract_collection#Iterator#finish (var_79) on <var_79:ArrayIterator[Object]> */
-RET_LABEL99:(void)0;
+{ /* Inline abstract_collection#Iterator#finish (var_80) on <var_80:ArrayIterator[nullable Object]> */
+RET_LABEL100:(void)0;
 }
 }
 {
-{ /* Inline poset#POSetElement#dtos (var_fe) on <var_fe:POSetElement[Object]> */
-var102 = var_fe->attrs[COLOR_poset__POSetElement___dtos].val; /* _dtos on <var_fe:POSetElement[Object]> */
-if (unlikely(var102 == NULL)) {
+{ /* Inline poset#POSetElement#dtos (var_fe) on <var_fe:POSetElement[nullable Object]> */
+var103 = var_fe->attrs[COLOR_poset__POSetElement___dtos].val; /* _dtos on <var_fe:POSetElement[nullable Object]> */
+if (unlikely(var103 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _dtos");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 247);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 391);
 show_backtrace(1);
 }
-var100 = var102;
-RET_LABEL101:(void)0;
+var101 = var103;
+RET_LABEL102:(void)0;
 }
 }
 {
-hash_collection__HashSet__add(var100, var_t); /* Direct call hash_collection#HashSet#add on <var100:HashSet[Object]>*/
+standard___standard__HashSet___standard__abstract_collection__SimpleCollection__add(var101, var_t); /* Direct call hash_collection#HashSet#add on <var101:HashSet[nullable Object]>*/
 }
 {
-{ /* Inline poset#POSetElement#dfroms (var_te) on <var_te:POSetElement[Object]> */
-var105 = var_te->attrs[COLOR_poset__POSetElement___dfroms].val; /* _dfroms on <var_te:POSetElement[Object]> */
-if (unlikely(var105 == NULL)) {
+{ /* Inline poset#POSetElement#dfroms (var_te) on <var_te:POSetElement[nullable Object]> */
+var106 = var_te->attrs[COLOR_poset__POSetElement___dfroms].val; /* _dfroms on <var_te:POSetElement[nullable Object]> */
+if (unlikely(var106 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _dfroms");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 248);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 392);
 show_backtrace(1);
 }
-var103 = var105;
-RET_LABEL104:(void)0;
+var104 = var106;
+RET_LABEL105:(void)0;
 }
 }
 {
-hash_collection__HashSet__add(var103, var_f); /* Direct call hash_collection#HashSet#add on <var103:HashSet[Object]>*/
+standard___standard__HashSet___standard__abstract_collection__SimpleCollection__add(var104, var_f); /* Direct call hash_collection#HashSet#add on <var104:HashSet[nullable Object]>*/
 }
 RET_LABEL:;
 }
-/* method poset#POSet#add_edge for (self: Object, Object, Object) */
-void VIRTUAL_poset__POSet__add_edge(val* self, val* p0, val* p1) {
-poset__POSet__add_edge(self, p0, p1); /* Direct call poset#POSet#add_edge on <self:Object(POSet[Object])>*/
-RET_LABEL:;
-}
-/* method poset#POSet#compare for (self: POSet[Object], Object, Object): Int */
-long poset__POSet__compare(val* self, val* p0, val* p1) {
+/* method poset#POSet#compare for (self: POSet[nullable Object], nullable Object, nullable Object): Int */
+long poset___poset__POSet___standard__sorter__Comparator__compare(val* self, val* p0, val* p1) {
 long var /* : Int */;
 short int var1 /* : Bool */;
 int cltype;
 int idtype;
 const struct type* type_struct;
+short int is_nullable;
 const char* var_class_name;
 short int var2 /* : Bool */;
 int cltype3;
 int idtype4;
 const struct type* type_struct5;
-const char* var_class_name6;
-val* var_a /* var a: Object */;
-val* var_b /* var b: Object */;
-val* var7 /* : HashMap[Object, POSetElement[Object]] */;
-val* var9 /* : HashMap[Object, POSetElement[Object]] */;
-val* var10 /* : nullable Object */;
-val* var_ae /* var ae: POSetElement[Object] */;
-val* var11 /* : HashMap[Object, POSetElement[Object]] */;
-val* var13 /* : HashMap[Object, POSetElement[Object]] */;
-val* var14 /* : nullable Object */;
-val* var_be /* var be: POSetElement[Object] */;
-val* var15 /* : HashSet[Object] */;
-val* var17 /* : HashSet[Object] */;
-long var18 /* : Int */;
-val* var19 /* : HashSet[Object] */;
-val* var21 /* : HashSet[Object] */;
-long var22 /* : Int */;
+short int is_nullable6;
+const char* var_class_name7;
+val* var_a /* var a: nullable Object */;
+val* var_b /* var b: nullable Object */;
+val* var8 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+val* var10 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+val* var11 /* : nullable Object */;
+val* var_ae /* var ae: POSetElement[nullable Object] */;
+val* var12 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+val* var14 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+val* var15 /* : nullable Object */;
+val* var_be /* var be: POSetElement[nullable Object] */;
+val* var16 /* : HashSet[nullable Object] */;
+val* var18 /* : HashSet[nullable Object] */;
+long var19 /* : Int */;
+val* var20 /* : HashSet[nullable Object] */;
+val* var22 /* : HashSet[nullable Object] */;
 long var23 /* : Int */;
-long var_res /* var res: Int */;
 long var24 /* : Int */;
-short int var25 /* : Bool */;
+long var_res /* var res: Int */;
+long var25 /* : Int */;
 short int var26 /* : Bool */;
 short int var28 /* : Bool */;
 short int var29 /* : Bool */;
-val* var30 /* : HashMap[Object, POSetElement[Object]] */;
-val* var32 /* : HashMap[Object, POSetElement[Object]] */;
+val* var30 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+val* var32 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
 val* var33 /* : nullable Object */;
 long var34 /* : Int */;
 long var36 /* : Int */;
-val* var37 /* : HashMap[Object, POSetElement[Object]] */;
-val* var39 /* : HashMap[Object, POSetElement[Object]] */;
+val* var37 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
+val* var39 /* : HashMap[nullable Object, POSetElement[nullable Object]] */;
 val* var40 /* : nullable Object */;
 long var41 /* : Int */;
 long var43 /* : Int */;
 long var44 /* : Int */;
-/* Covariant cast for argument 0 (a) <p0:Object> isa E */
-/* <p0:Object> isa E */
-type_struct = self->type->resolution_table->types[COLOR_poset__POSet_FT0];
+/* Covariant cast for argument 0 (a) <p0:nullable Object> isa E */
+/* <p0:nullable Object> isa E */
+type_struct = self->type->resolution_table->types[COLOR_poset__POSet___35dE];
 cltype = type_struct->color;
 idtype = type_struct->id;
+is_nullable = type_struct->is_nullable;
+if(p0 == NULL) {
+var1 = is_nullable;
+} else {
 if(cltype >= p0->type->table_size) {
 var1 = 0;
 } else {
 var1 = p0->type->type_table[cltype] == idtype;
 }
+}
 if (unlikely(!var1)) {
 var_class_name = p0 == NULL ? "null" : p0->type->name;
 PRINT_ERROR("Runtime error: Cast failed. Expected `%s`, got `%s`", "E", var_class_name);
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 153);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 267);
 show_backtrace(1);
 }
-/* Covariant cast for argument 1 (b) <p1:Object> isa E */
-/* <p1:Object> isa E */
-type_struct5 = self->type->resolution_table->types[COLOR_poset__POSet_FT0];
+/* Covariant cast for argument 1 (b) <p1:nullable Object> isa E */
+/* <p1:nullable Object> isa E */
+type_struct5 = self->type->resolution_table->types[COLOR_poset__POSet___35dE];
 cltype3 = type_struct5->color;
 idtype4 = type_struct5->id;
+is_nullable6 = type_struct5->is_nullable;
+if(p1 == NULL) {
+var2 = is_nullable6;
+} else {
 if(cltype3 >= p1->type->table_size) {
 var2 = 0;
 } else {
 var2 = p1->type->type_table[cltype3] == idtype4;
 }
+}
 if (unlikely(!var2)) {
-var_class_name6 = p1 == NULL ? "null" : p1->type->name;
-PRINT_ERROR("Runtime error: Cast failed. Expected `%s`, got `%s`", "E", var_class_name6);
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 153);
+var_class_name7 = p1 == NULL ? "null" : p1->type->name;
+PRINT_ERROR("Runtime error: Cast failed. Expected `%s`, got `%s`", "E", var_class_name7);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 267);
 show_backtrace(1);
 }
 var_a = p0;
 var_b = p1;
 {
-{ /* Inline poset#POSet#elements (self) on <self:POSet[Object]> */
-var9 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[Object]> */
-if (unlikely(var9 == NULL)) {
+{ /* Inline poset#POSet#elements (self) on <self:POSet[nullable Object]> */
+var10 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[nullable Object]> */
+if (unlikely(var10 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _elements");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 33);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 82);
 show_backtrace(1);
 }
-var7 = var9;
-RET_LABEL8:(void)0;
+var8 = var10;
+RET_LABEL9:(void)0;
 }
 }
 {
-var10 = hash_collection__HashMap___91d_93d(var7, var_a);
+var11 = standard___standard__HashMap___standard__abstract_collection__MapRead___91d_93d(var8, var_a);
 }
-var_ae = var10;
+var_ae = var11;
 {
-{ /* Inline poset#POSet#elements (self) on <self:POSet[Object]> */
-var13 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[Object]> */
-if (unlikely(var13 == NULL)) {
+{ /* Inline poset#POSet#elements (self) on <self:POSet[nullable Object]> */
+var14 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[nullable Object]> */
+if (unlikely(var14 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _elements");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 33);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 82);
 show_backtrace(1);
 }
-var11 = var13;
-RET_LABEL12:(void)0;
+var12 = var14;
+RET_LABEL13:(void)0;
 }
 }
 {
-var14 = hash_collection__HashMap___91d_93d(var11, var_b);
+var15 = standard___standard__HashMap___standard__abstract_collection__MapRead___91d_93d(var12, var_b);
 }
-var_be = var14;
+var_be = var15;
 {
-{ /* Inline poset#POSetElement#tos (var_ae) on <var_ae:POSetElement[Object]> */
-var17 = var_ae->attrs[COLOR_poset__POSetElement___tos].val; /* _tos on <var_ae:POSetElement[Object]> */
-if (unlikely(var17 == NULL)) {
+{ /* Inline poset#POSetElement#tos (var_ae) on <var_ae:POSetElement[nullable Object]> */
+var18 = var_ae->attrs[COLOR_poset__POSetElement___tos].val; /* _tos on <var_ae:POSetElement[nullable Object]> */
+if (unlikely(var18 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _tos");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 245);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 389);
 show_backtrace(1);
 }
-var15 = var17;
-RET_LABEL16:(void)0;
+var16 = var18;
+RET_LABEL17:(void)0;
 }
 }
 {
-var18 = hash_collection__HashSet__length(var15);
+var19 = standard___standard__HashSet___standard__abstract_collection__Collection__length(var16);
 }
 {
-{ /* Inline poset#POSetElement#tos (var_be) on <var_be:POSetElement[Object]> */
-var21 = var_be->attrs[COLOR_poset__POSetElement___tos].val; /* _tos on <var_be:POSetElement[Object]> */
-if (unlikely(var21 == NULL)) {
+{ /* Inline poset#POSetElement#tos (var_be) on <var_be:POSetElement[nullable Object]> */
+var22 = var_be->attrs[COLOR_poset__POSetElement___tos].val; /* _tos on <var_be:POSetElement[nullable Object]> */
+if (unlikely(var22 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _tos");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 245);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 389);
 show_backtrace(1);
 }
-var19 = var21;
-RET_LABEL20:(void)0;
+var20 = var22;
+RET_LABEL21:(void)0;
 }
 }
 {
-var22 = hash_collection__HashSet__length(var19);
+var23 = standard___standard__HashSet___standard__abstract_collection__Collection__length(var20);
 }
 {
-var23 = kernel__Int___60d_61d_62d(var18, var22);
+var24 = standard___standard__Int___Comparable___60d_61d_62d(var19, var23);
 }
-var_res = var23;
-var24 = 0;
+var_res = var24;
+var25 = 0;
 {
-{ /* Inline kernel#Int#!= (var_res,var24) on <var_res:Int> */
-var28 = var_res == var24;
+{ /* Inline kernel#Int#!= (var_res,var25) on <var_res:Int> */
+var28 = var_res == var25;
 var29 = !var28;
 var26 = var29;
 goto RET_LABEL27;
 RET_LABEL27:(void)0;
 }
-var25 = var26;
 }
-if (var25){
+if (var26){
 var = var_res;
 goto RET_LABEL;
 } else {
 }
 {
-{ /* Inline poset#POSet#elements (self) on <self:POSet[Object]> */
-var32 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[Object]> */
+{ /* Inline poset#POSet#elements (self) on <self:POSet[nullable Object]> */
+var32 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[nullable Object]> */
 if (unlikely(var32 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _elements");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 33);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 82);
 show_backtrace(1);
 }
 var30 = var32;
@@ -1169,21 +1149,21 @@ RET_LABEL31:(void)0;
 }
 }
 {
-var33 = hash_collection__HashMap___91d_93d(var30, var_a);
+var33 = standard___standard__HashMap___standard__abstract_collection__MapRead___91d_93d(var30, var_a);
 }
 {
-{ /* Inline poset#POSetElement#count (var33) on <var33:nullable Object(POSetElement[Object])> */
-var36 = var33->attrs[COLOR_poset__POSetElement___count].l; /* _count on <var33:nullable Object(POSetElement[Object])> */
+{ /* Inline poset#POSetElement#count (var33) on <var33:nullable Object(POSetElement[nullable Object])> */
+var36 = var33->attrs[COLOR_poset__POSetElement___count].l; /* _count on <var33:nullable Object(POSetElement[nullable Object])> */
 var34 = var36;
 RET_LABEL35:(void)0;
 }
 }
 {
-{ /* Inline poset#POSet#elements (self) on <self:POSet[Object]> */
-var39 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[Object]> */
+{ /* Inline poset#POSet#elements (self) on <self:POSet[nullable Object]> */
+var39 = self->attrs[COLOR_poset__POSet___elements].val; /* _elements on <self:POSet[nullable Object]> */
 if (unlikely(var39 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _elements");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 33);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 82);
 show_backtrace(1);
 }
 var37 = var39;
@@ -1191,46 +1171,37 @@ RET_LABEL38:(void)0;
 }
 }
 {
-var40 = hash_collection__HashMap___91d_93d(var37, var_b);
+var40 = standard___standard__HashMap___standard__abstract_collection__MapRead___91d_93d(var37, var_b);
 }
 {
-{ /* Inline poset#POSetElement#count (var40) on <var40:nullable Object(POSetElement[Object])> */
-var43 = var40->attrs[COLOR_poset__POSetElement___count].l; /* _count on <var40:nullable Object(POSetElement[Object])> */
+{ /* Inline poset#POSetElement#count (var40) on <var40:nullable Object(POSetElement[nullable Object])> */
+var43 = var40->attrs[COLOR_poset__POSetElement___count].l; /* _count on <var40:nullable Object(POSetElement[nullable Object])> */
 var41 = var43;
 RET_LABEL42:(void)0;
 }
 }
 {
-var44 = kernel__Int___60d_61d_62d(var34, var41);
+var44 = standard___standard__Int___Comparable___60d_61d_62d(var34, var41);
 }
 var = var44;
 goto RET_LABEL;
 RET_LABEL:;
 return var;
 }
-/* method poset#POSet#compare for (self: Object, nullable Object, nullable Object): Int */
-long VIRTUAL_poset__POSet__compare(val* self, val* p0, val* p1) {
-long var /* : Int */;
-long var1 /* : Int */;
-var1 = poset__POSet__compare(self, p0, p1);
-var = var1;
-RET_LABEL:;
-return var;
-}
-/* method poset#POSet#linearize for (self: POSet[Object], Collection[Object]): Array[Object] */
-val* poset__POSet__linearize(val* self, val* p0) {
-val* var /* : Array[Object] */;
+/* method poset#POSet#linearize for (self: POSet[nullable Object], Collection[nullable Object]): Array[nullable Object] */
+val* poset___poset__POSet___linearize(val* self, val* p0) {
+val* var /* : Array[nullable Object] */;
 short int var1 /* : Bool */;
 int cltype;
 int idtype;
 const struct type* type_struct;
 const char* var_class_name;
-val* var_elements /* var elements: Collection[Object] */;
+val* var_elements /* var elements: Collection[nullable Object] */;
 val* var2 /* : Array[nullable Object] */;
-val* var_lin /* var lin: Array[Object] */;
-/* Covariant cast for argument 0 (elements) <p0:Collection[Object]> isa Collection[E] */
-/* <p0:Collection[Object]> isa Collection[E] */
-type_struct = self->type->resolution_table->types[COLOR_abstract_collection__Collectionposet__POSet_FT0];
+val* var_lin /* var lin: Array[nullable Object] */;
+/* Covariant cast for argument 0 (elements) <p0:Collection[nullable Object]> isa Collection[E] */
+/* <p0:Collection[nullable Object]> isa Collection[E] */
+type_struct = self->type->resolution_table->types[COLOR_standard__Collection__poset__POSet___35dE];
 cltype = type_struct->color;
 idtype = type_struct->id;
 if(cltype >= p0->type->table_size) {
@@ -1241,74 +1212,46 @@ var1 = p0->type->type_table[cltype] == idtype;
 if (unlikely(!var1)) {
 var_class_name = p0 == NULL ? "null" : p0->type->name;
 PRINT_ERROR("Runtime error: Cast failed. Expected `%s`, got `%s`", "Collection[E]", var_class_name);
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 218);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 353);
 show_backtrace(1);
 }
 var_elements = p0;
 {
-var2 = array__Collection__to_a(var_elements);
+var2 = standard__array___Collection___to_a(var_elements);
 }
 var_lin = var2;
 {
-sorter__Comparator__sort(self, var_lin); /* Direct call sorter#Comparator#sort on <self:POSet[Object]>*/
+standard___standard__Comparator___sort(self, var_lin); /* Direct call sorter#Comparator#sort on <self:POSet[nullable Object]>*/
 }
 var = var_lin;
 goto RET_LABEL;
 RET_LABEL:;
 return var;
 }
-/* method poset#POSet#linearize for (self: Object, Collection[Object]): Array[Object] */
-val* VIRTUAL_poset__POSet__linearize(val* self, val* p0) {
-val* var /* : Array[Object] */;
-val* var1 /* : Array[Object] */;
-var1 = poset__POSet__linearize(self, p0);
-var = var1;
-RET_LABEL:;
-return var;
-}
-/* method poset#POSetElement#poset for (self: POSetElement[Object]): POSet[Object] */
-val* poset__POSetElement__poset(val* self) {
-val* var /* : POSet[Object] */;
-val* var1 /* : POSet[Object] */;
-var1 = self->attrs[COLOR_poset__POSetElement___poset].val; /* _poset on <self:POSetElement[Object]> */
+/* method poset#POSetElement#poset for (self: POSetElement[nullable Object]): POSet[nullable Object] */
+val* poset___poset__POSetElement___poset(val* self) {
+val* var /* : POSet[nullable Object] */;
+val* var1 /* : POSet[nullable Object] */;
+var1 = self->attrs[COLOR_poset__POSetElement___poset].val; /* _poset on <self:POSetElement[nullable Object]> */
 if (unlikely(var1 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _poset");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 239);
-show_backtrace(1);
-}
-var = var1;
-RET_LABEL:;
-return var;
-}
-/* method poset#POSetElement#poset for (self: Object): POSet[Object] */
-val* VIRTUAL_poset__POSetElement__poset(val* self) {
-val* var /* : POSet[Object] */;
-val* var1 /* : POSet[Object] */;
-val* var3 /* : POSet[Object] */;
-{ /* Inline poset#POSetElement#poset (self) on <self:Object(POSetElement[Object])> */
-var3 = self->attrs[COLOR_poset__POSetElement___poset].val; /* _poset on <self:Object(POSetElement[Object])> */
-if (unlikely(var3 == NULL)) {
-PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _poset");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 239);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 383);
 show_backtrace(1);
 }
-var1 = var3;
-RET_LABEL2:(void)0;
-}
 var = var1;
 RET_LABEL:;
 return var;
 }
-/* method poset#POSetElement#poset= for (self: POSetElement[Object], POSet[Object]) */
-void poset__POSetElement__poset_61d(val* self, val* p0) {
+/* method poset#POSetElement#poset= for (self: POSetElement[nullable Object], POSet[nullable Object]) */
+void poset___poset__POSetElement___poset_61d(val* self, val* p0) {
 short int var /* : Bool */;
 int cltype;
 int idtype;
 const struct type* type_struct;
 const char* var_class_name;
-/* Covariant cast for argument 0 (poset) <p0:POSet[Object]> isa POSet[E] */
-/* <p0:POSet[Object]> isa POSet[E] */
-type_struct = self->type->resolution_table->types[COLOR_poset__POSetposet__POSetElement_FT0];
+/* Covariant cast for argument 0 (poset) <p0:POSet[nullable Object]> isa POSet[E] */
+/* <p0:POSet[nullable Object]> isa POSet[E] */
+type_struct = self->type->resolution_table->types[COLOR_poset__POSet__poset__POSetElement___35dE];
 cltype = type_struct->color;
 idtype = type_struct->id;
 if(cltype >= p0->type->table_size) {
@@ -1319,308 +1262,134 @@ var = p0->type->type_table[cltype] == idtype;
 if (unlikely(!var)) {
 var_class_name = p0 == NULL ? "null" : p0->type->name;
 PRINT_ERROR("Runtime error: Cast failed. Expected `%s`, got `%s`", "POSet[E]", var_class_name);
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 239);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 383);
 show_backtrace(1);
 }
-self->attrs[COLOR_poset__POSetElement___poset].val = p0; /* _poset on <self:POSetElement[Object]> */
+self->attrs[COLOR_poset__POSetElement___poset].val = p0; /* _poset on <self:POSetElement[nullable Object]> */
 RET_LABEL:;
 }
-/* method poset#POSetElement#poset= for (self: Object, POSet[Object]) */
-void VIRTUAL_poset__POSetElement__poset_61d(val* self, val* p0) {
-short int var /* : Bool */;
-int cltype;
-int idtype;
-const struct type* type_struct;
-const char* var_class_name;
-{ /* Inline poset#POSetElement#poset= (self,p0) on <self:Object(POSetElement[Object])> */
-/* Covariant cast for argument 0 (poset) <p0:POSet[Object]> isa POSet[E] */
-/* <p0:POSet[Object]> isa POSet[E] */
-type_struct = self->type->resolution_table->types[COLOR_poset__POSetposet__POSetElement_FT0];
-cltype = type_struct->color;
-idtype = type_struct->id;
-if(cltype >= p0->type->table_size) {
-var = 0;
-} else {
-var = p0->type->type_table[cltype] == idtype;
-}
-if (unlikely(!var)) {
-var_class_name = p0 == NULL ? "null" : p0->type->name;
-PRINT_ERROR("Runtime error: Cast failed. Expected `%s`, got `%s`", "POSet[E]", var_class_name);
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 239);
-show_backtrace(1);
-}
-self->attrs[COLOR_poset__POSetElement___poset].val = p0; /* _poset on <self:Object(POSetElement[Object])> */
-RET_LABEL1:(void)0;
-}
-RET_LABEL:;
-}
-/* method poset#POSetElement#element for (self: POSetElement[Object]): Object */
-val* poset__POSetElement__element(val* self) {
-val* var /* : Object */;
-val* var1 /* : Object */;
-var1 = self->attrs[COLOR_poset__POSetElement___element].val; /* _element on <self:POSetElement[Object]> */
-if (unlikely(var1 == NULL)) {
-PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _element");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 242);
-show_backtrace(1);
-}
+/* method poset#POSetElement#element for (self: POSetElement[nullable Object]): nullable Object */
+val* poset___poset__POSetElement___element(val* self) {
+val* var /* : nullable Object */;
+val* var1 /* : nullable Object */;
+var1 = self->attrs[COLOR_poset__POSetElement___element].val; /* _element on <self:POSetElement[nullable Object]> */
 var = var1;
 RET_LABEL:;
 return var;
 }
-/* method poset#POSetElement#element for (self: Object): Object */
-val* VIRTUAL_poset__POSetElement__element(val* self) {
-val* var /* : Object */;
-val* var1 /* : Object */;
-val* var3 /* : Object */;
-{ /* Inline poset#POSetElement#element (self) on <self:Object(POSetElement[Object])> */
-var3 = self->attrs[COLOR_poset__POSetElement___element].val; /* _element on <self:Object(POSetElement[Object])> */
-if (unlikely(var3 == NULL)) {
-PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _element");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 242);
-show_backtrace(1);
-}
-var1 = var3;
-RET_LABEL2:(void)0;
-}
-var = var1;
-RET_LABEL:;
-return var;
-}
-/* method poset#POSetElement#element= for (self: POSetElement[Object], Object) */
-void poset__POSetElement__element_61d(val* self, val* p0) {
+/* method poset#POSetElement#element= for (self: POSetElement[nullable Object], nullable Object) */
+void poset___poset__POSetElement___element_61d(val* self, val* p0) {
 short int var /* : Bool */;
 int cltype;
 int idtype;
 const struct type* type_struct;
+short int is_nullable;
 const char* var_class_name;
-/* Covariant cast for argument 0 (element) <p0:Object> isa E */
-/* <p0:Object> isa E */
-type_struct = self->type->resolution_table->types[COLOR_poset__POSetElement_FT0];
+/* Covariant cast for argument 0 (element) <p0:nullable Object> isa E */
+/* <p0:nullable Object> isa E */
+type_struct = self->type->resolution_table->types[COLOR_poset__POSetElement___35dE];
 cltype = type_struct->color;
 idtype = type_struct->id;
-if(cltype >= p0->type->table_size) {
-var = 0;
+is_nullable = type_struct->is_nullable;
+if(p0 == NULL) {
+var = is_nullable;
 } else {
-var = p0->type->type_table[cltype] == idtype;
-}
-if (unlikely(!var)) {
-var_class_name = p0 == NULL ? "null" : p0->type->name;
-PRINT_ERROR("Runtime error: Cast failed. Expected `%s`, got `%s`", "E", var_class_name);
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 242);
-show_backtrace(1);
-}
-self->attrs[COLOR_poset__POSetElement___element].val = p0; /* _element on <self:POSetElement[Object]> */
-RET_LABEL:;
-}
-/* method poset#POSetElement#element= for (self: Object, Object) */
-void VIRTUAL_poset__POSetElement__element_61d(val* self, val* p0) {
-short int var /* : Bool */;
-int cltype;
-int idtype;
-const struct type* type_struct;
-const char* var_class_name;
-{ /* Inline poset#POSetElement#element= (self,p0) on <self:Object(POSetElement[Object])> */
-/* Covariant cast for argument 0 (element) <p0:Object> isa E */
-/* <p0:Object> isa E */
-type_struct = self->type->resolution_table->types[COLOR_poset__POSetElement_FT0];
-cltype = type_struct->color;
-idtype = type_struct->id;
 if(cltype >= p0->type->table_size) {
 var = 0;
 } else {
 var = p0->type->type_table[cltype] == idtype;
 }
+}
 if (unlikely(!var)) {
 var_class_name = p0 == NULL ? "null" : p0->type->name;
 PRINT_ERROR("Runtime error: Cast failed. Expected `%s`, got `%s`", "E", var_class_name);
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 242);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 386);
 show_backtrace(1);
 }
-self->attrs[COLOR_poset__POSetElement___element].val = p0; /* _element on <self:Object(POSetElement[Object])> */
-RET_LABEL1:(void)0;
-}
+self->attrs[COLOR_poset__POSetElement___element].val = p0; /* _element on <self:POSetElement[nullable Object]> */
 RET_LABEL:;
 }
-/* method poset#POSetElement#tos for (self: POSetElement[Object]): HashSet[Object] */
-val* poset__POSetElement__tos(val* self) {
-val* var /* : HashSet[Object] */;
-val* var1 /* : HashSet[Object] */;
-var1 = self->attrs[COLOR_poset__POSetElement___tos].val; /* _tos on <self:POSetElement[Object]> */
+/* method poset#POSetElement#tos for (self: POSetElement[nullable Object]): HashSet[nullable Object] */
+val* poset___poset__POSetElement___tos(val* self) {
+val* var /* : HashSet[nullable Object] */;
+val* var1 /* : HashSet[nullable Object] */;
+var1 = self->attrs[COLOR_poset__POSetElement___tos].val; /* _tos on <self:POSetElement[nullable Object]> */
 if (unlikely(var1 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _tos");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 245);
-show_backtrace(1);
-}
-var = var1;
-RET_LABEL:;
-return var;
-}
-/* method poset#POSetElement#tos for (self: Object): HashSet[Object] */
-val* VIRTUAL_poset__POSetElement__tos(val* self) {
-val* var /* : HashSet[Object] */;
-val* var1 /* : HashSet[Object] */;
-val* var3 /* : HashSet[Object] */;
-{ /* Inline poset#POSetElement#tos (self) on <self:Object(POSetElement[Object])> */
-var3 = self->attrs[COLOR_poset__POSetElement___tos].val; /* _tos on <self:Object(POSetElement[Object])> */
-if (unlikely(var3 == NULL)) {
-PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _tos");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 245);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 389);
 show_backtrace(1);
 }
-var1 = var3;
-RET_LABEL2:(void)0;
-}
 var = var1;
 RET_LABEL:;
 return var;
 }
-/* method poset#POSetElement#froms for (self: POSetElement[Object]): HashSet[Object] */
-val* poset__POSetElement__froms(val* self) {
-val* var /* : HashSet[Object] */;
-val* var1 /* : HashSet[Object] */;
-var1 = self->attrs[COLOR_poset__POSetElement___froms].val; /* _froms on <self:POSetElement[Object]> */
+/* method poset#POSetElement#froms for (self: POSetElement[nullable Object]): HashSet[nullable Object] */
+val* poset___poset__POSetElement___froms(val* self) {
+val* var /* : HashSet[nullable Object] */;
+val* var1 /* : HashSet[nullable Object] */;
+var1 = self->attrs[COLOR_poset__POSetElement___froms].val; /* _froms on <self:POSetElement[nullable Object]> */
 if (unlikely(var1 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _froms");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 246);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 390);
 show_backtrace(1);
 }
 var = var1;
 RET_LABEL:;
 return var;
 }
-/* method poset#POSetElement#froms for (self: Object): HashSet[Object] */
-val* VIRTUAL_poset__POSetElement__froms(val* self) {
-val* var /* : HashSet[Object] */;
-val* var1 /* : HashSet[Object] */;
-val* var3 /* : HashSet[Object] */;
-{ /* Inline poset#POSetElement#froms (self) on <self:Object(POSetElement[Object])> */
-var3 = self->attrs[COLOR_poset__POSetElement___froms].val; /* _froms on <self:Object(POSetElement[Object])> */
-if (unlikely(var3 == NULL)) {
-PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _froms");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 246);
-show_backtrace(1);
-}
-var1 = var3;
-RET_LABEL2:(void)0;
-}
-var = var1;
-RET_LABEL:;
-return var;
-}
-/* method poset#POSetElement#dtos for (self: POSetElement[Object]): HashSet[Object] */
-val* poset__POSetElement__dtos(val* self) {
-val* var /* : HashSet[Object] */;
-val* var1 /* : HashSet[Object] */;
-var1 = self->attrs[COLOR_poset__POSetElement___dtos].val; /* _dtos on <self:POSetElement[Object]> */
+/* method poset#POSetElement#dtos for (self: POSetElement[nullable Object]): HashSet[nullable Object] */
+val* poset___poset__POSetElement___dtos(val* self) {
+val* var /* : HashSet[nullable Object] */;
+val* var1 /* : HashSet[nullable Object] */;
+var1 = self->attrs[COLOR_poset__POSetElement___dtos].val; /* _dtos on <self:POSetElement[nullable Object]> */
 if (unlikely(var1 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _dtos");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 247);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 391);
 show_backtrace(1);
 }
 var = var1;
 RET_LABEL:;
 return var;
 }
-/* method poset#POSetElement#dtos for (self: Object): HashSet[Object] */
-val* VIRTUAL_poset__POSetElement__dtos(val* self) {
-val* var /* : HashSet[Object] */;
-val* var1 /* : HashSet[Object] */;
-val* var3 /* : HashSet[Object] */;
-{ /* Inline poset#POSetElement#dtos (self) on <self:Object(POSetElement[Object])> */
-var3 = self->attrs[COLOR_poset__POSetElement___dtos].val; /* _dtos on <self:Object(POSetElement[Object])> */
-if (unlikely(var3 == NULL)) {
-PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _dtos");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 247);
-show_backtrace(1);
-}
-var1 = var3;
-RET_LABEL2:(void)0;
-}
-var = var1;
-RET_LABEL:;
-return var;
-}
-/* method poset#POSetElement#dfroms for (self: POSetElement[Object]): HashSet[Object] */
-val* poset__POSetElement__dfroms(val* self) {
-val* var /* : HashSet[Object] */;
-val* var1 /* : HashSet[Object] */;
-var1 = self->attrs[COLOR_poset__POSetElement___dfroms].val; /* _dfroms on <self:POSetElement[Object]> */
+/* method poset#POSetElement#dfroms for (self: POSetElement[nullable Object]): HashSet[nullable Object] */
+val* poset___poset__POSetElement___dfroms(val* self) {
+val* var /* : HashSet[nullable Object] */;
+val* var1 /* : HashSet[nullable Object] */;
+var1 = self->attrs[COLOR_poset__POSetElement___dfroms].val; /* _dfroms on <self:POSetElement[nullable Object]> */
 if (unlikely(var1 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _dfroms");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 248);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 392);
 show_backtrace(1);
 }
 var = var1;
 RET_LABEL:;
 return var;
 }
-/* method poset#POSetElement#dfroms for (self: Object): HashSet[Object] */
-val* VIRTUAL_poset__POSetElement__dfroms(val* self) {
-val* var /* : HashSet[Object] */;
-val* var1 /* : HashSet[Object] */;
-val* var3 /* : HashSet[Object] */;
-{ /* Inline poset#POSetElement#dfroms (self) on <self:Object(POSetElement[Object])> */
-var3 = self->attrs[COLOR_poset__POSetElement___dfroms].val; /* _dfroms on <self:Object(POSetElement[Object])> */
-if (unlikely(var3 == NULL)) {
-PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _dfroms");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 248);
-show_backtrace(1);
-}
-var1 = var3;
-RET_LABEL2:(void)0;
-}
-var = var1;
-RET_LABEL:;
-return var;
-}
-/* method poset#POSetElement#count for (self: POSetElement[Object]): Int */
-long poset__POSetElement__count(val* self) {
+/* method poset#POSetElement#count for (self: POSetElement[nullable Object]): Int */
+long poset___poset__POSetElement___count(val* self) {
 long var /* : Int */;
 long var1 /* : Int */;
-var1 = self->attrs[COLOR_poset__POSetElement___count].l; /* _count on <self:POSetElement[Object]> */
+var1 = self->attrs[COLOR_poset__POSetElement___count].l; /* _count on <self:POSetElement[nullable Object]> */
 var = var1;
 RET_LABEL:;
 return var;
 }
-/* method poset#POSetElement#count for (self: Object): Int */
-long VIRTUAL_poset__POSetElement__count(val* self) {
-long var /* : Int */;
-long var1 /* : Int */;
-long var3 /* : Int */;
-{ /* Inline poset#POSetElement#count (self) on <self:Object(POSetElement[Object])> */
-var3 = self->attrs[COLOR_poset__POSetElement___count].l; /* _count on <self:Object(POSetElement[Object])> */
-var1 = var3;
-RET_LABEL2:(void)0;
-}
-var = var1;
+/* method poset#POSetElement#count= for (self: POSetElement[nullable Object], Int) */
+void poset___poset__POSetElement___count_61d(val* self, long p0) {
+self->attrs[COLOR_poset__POSetElement___count].l = p0; /* _count on <self:POSetElement[nullable Object]> */
 RET_LABEL:;
-return var;
 }
-/* method poset#POSetElement#count= for (self: POSetElement[Object], Int) */
-void poset__POSetElement__count_61d(val* self, long p0) {
-self->attrs[COLOR_poset__POSetElement___count].l = p0; /* _count on <self:POSetElement[Object]> */
-RET_LABEL:;
-}
-/* method poset#POSetElement#count= for (self: Object, Int) */
-void VIRTUAL_poset__POSetElement__count_61d(val* self, long p0) {
-{ /* Inline poset#POSetElement#count= (self,p0) on <self:Object(POSetElement[Object])> */
-self->attrs[COLOR_poset__POSetElement___count].l = p0; /* _count on <self:Object(POSetElement[Object])> */
-RET_LABEL1:(void)0;
-}
-RET_LABEL:;
-}
-/* method poset#POSetElement#greaters for (self: POSetElement[Object]): Collection[Object] */
-val* poset__POSetElement__greaters(val* self) {
-val* var /* : Collection[Object] */;
-val* var1 /* : HashSet[Object] */;
-val* var3 /* : HashSet[Object] */;
+/* method poset#POSetElement#greaters for (self: POSetElement[nullable Object]): Collection[nullable Object] */
+val* poset___poset__POSetElement___greaters(val* self) {
+val* var /* : Collection[nullable Object] */;
+val* var1 /* : HashSet[nullable Object] */;
+val* var3 /* : HashSet[nullable Object] */;
 {
-{ /* Inline poset#POSetElement#tos (self) on <self:POSetElement[Object]> */
-var3 = self->attrs[COLOR_poset__POSetElement___tos].val; /* _tos on <self:POSetElement[Object]> */
+{ /* Inline poset#POSetElement#tos (self) on <self:POSetElement[nullable Object]> */
+var3 = self->attrs[COLOR_poset__POSetElement___tos].val; /* _tos on <self:POSetElement[nullable Object]> */
 if (unlikely(var3 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _tos");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 245);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 389);
 show_backtrace(1);
 }
 var1 = var3;
@@ -1632,26 +1401,17 @@ goto RET_LABEL;
 RET_LABEL:;
 return var;
 }
-/* method poset#POSetElement#greaters for (self: Object): Collection[Object] */
-val* VIRTUAL_poset__POSetElement__greaters(val* self) {
-val* var /* : Collection[Object] */;
-val* var1 /* : Collection[Object] */;
-var1 = poset__POSetElement__greaters(self);
-var = var1;
-RET_LABEL:;
-return var;
-}
-/* method poset#POSetElement#direct_greaters for (self: POSetElement[Object]): Collection[Object] */
-val* poset__POSetElement__direct_greaters(val* self) {
-val* var /* : Collection[Object] */;
-val* var1 /* : HashSet[Object] */;
-val* var3 /* : HashSet[Object] */;
+/* method poset#POSetElement#direct_greaters for (self: POSetElement[nullable Object]): Collection[nullable Object] */
+val* poset___poset__POSetElement___direct_greaters(val* self) {
+val* var /* : Collection[nullable Object] */;
+val* var1 /* : HashSet[nullable Object] */;
+val* var3 /* : HashSet[nullable Object] */;
 {
-{ /* Inline poset#POSetElement#dtos (self) on <self:POSetElement[Object]> */
-var3 = self->attrs[COLOR_poset__POSetElement___dtos].val; /* _dtos on <self:POSetElement[Object]> */
+{ /* Inline poset#POSetElement#dtos (self) on <self:POSetElement[nullable Object]> */
+var3 = self->attrs[COLOR_poset__POSetElement___dtos].val; /* _dtos on <self:POSetElement[nullable Object]> */
 if (unlikely(var3 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _dtos");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 247);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 391);
 show_backtrace(1);
 }
 var1 = var3;
@@ -1663,26 +1423,17 @@ goto RET_LABEL;
 RET_LABEL:;
 return var;
 }
-/* method poset#POSetElement#direct_greaters for (self: Object): Collection[Object] */
-val* VIRTUAL_poset__POSetElement__direct_greaters(val* self) {
-val* var /* : Collection[Object] */;
-val* var1 /* : Collection[Object] */;
-var1 = poset__POSetElement__direct_greaters(self);
-var = var1;
-RET_LABEL:;
-return var;
-}
-/* method poset#POSetElement#smallers for (self: POSetElement[Object]): Collection[Object] */
-val* poset__POSetElement__smallers(val* self) {
-val* var /* : Collection[Object] */;
-val* var1 /* : HashSet[Object] */;
-val* var3 /* : HashSet[Object] */;
+/* method poset#POSetElement#smallers for (self: POSetElement[nullable Object]): Collection[nullable Object] */
+val* poset___poset__POSetElement___smallers(val* self) {
+val* var /* : Collection[nullable Object] */;
+val* var1 /* : HashSet[nullable Object] */;
+val* var3 /* : HashSet[nullable Object] */;
 {
-{ /* Inline poset#POSetElement#froms (self) on <self:POSetElement[Object]> */
-var3 = self->attrs[COLOR_poset__POSetElement___froms].val; /* _froms on <self:POSetElement[Object]> */
+{ /* Inline poset#POSetElement#froms (self) on <self:POSetElement[nullable Object]> */
+var3 = self->attrs[COLOR_poset__POSetElement___froms].val; /* _froms on <self:POSetElement[nullable Object]> */
 if (unlikely(var3 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _froms");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 246);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 390);
 show_backtrace(1);
 }
 var1 = var3;
@@ -1694,26 +1445,17 @@ goto RET_LABEL;
 RET_LABEL:;
 return var;
 }
-/* method poset#POSetElement#smallers for (self: Object): Collection[Object] */
-val* VIRTUAL_poset__POSetElement__smallers(val* self) {
-val* var /* : Collection[Object] */;
-val* var1 /* : Collection[Object] */;
-var1 = poset__POSetElement__smallers(self);
-var = var1;
-RET_LABEL:;
-return var;
-}
-/* method poset#POSetElement#direct_smallers for (self: POSetElement[Object]): Collection[Object] */
-val* poset__POSetElement__direct_smallers(val* self) {
-val* var /* : Collection[Object] */;
-val* var1 /* : HashSet[Object] */;
-val* var3 /* : HashSet[Object] */;
+/* method poset#POSetElement#direct_smallers for (self: POSetElement[nullable Object]): Collection[nullable Object] */
+val* poset___poset__POSetElement___direct_smallers(val* self) {
+val* var /* : Collection[nullable Object] */;
+val* var1 /* : HashSet[nullable Object] */;
+val* var3 /* : HashSet[nullable Object] */;
 {
-{ /* Inline poset#POSetElement#dfroms (self) on <self:POSetElement[Object]> */
-var3 = self->attrs[COLOR_poset__POSetElement___dfroms].val; /* _dfroms on <self:POSetElement[Object]> */
+{ /* Inline poset#POSetElement#dfroms (self) on <self:POSetElement[nullable Object]> */
+var3 = self->attrs[COLOR_poset__POSetElement___dfroms].val; /* _dfroms on <self:POSetElement[nullable Object]> */
 if (unlikely(var3 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _dfroms");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 248);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 392);
 show_backtrace(1);
 }
 var1 = var3;
@@ -1725,50 +1467,47 @@ goto RET_LABEL;
 RET_LABEL:;
 return var;
 }
-/* method poset#POSetElement#direct_smallers for (self: Object): Collection[Object] */
-val* VIRTUAL_poset__POSetElement__direct_smallers(val* self) {
-val* var /* : Collection[Object] */;
-val* var1 /* : Collection[Object] */;
-var1 = poset__POSetElement__direct_smallers(self);
-var = var1;
-RET_LABEL:;
-return var;
-}
-/* method poset#POSetElement#<= for (self: POSetElement[Object], Object): Bool */
-short int poset__POSetElement___60d_61d(val* self, val* p0) {
+/* method poset#POSetElement#<= for (self: POSetElement[nullable Object], nullable Object): Bool */
+short int poset___poset__POSetElement____60d_61d(val* self, val* p0) {
 short int var /* : Bool */;
 short int var1 /* : Bool */;
 int cltype;
 int idtype;
 const struct type* type_struct;
+short int is_nullable;
 const char* var_class_name;
-val* var_t /* var t: Object */;
-val* var2 /* : HashSet[Object] */;
-val* var4 /* : HashSet[Object] */;
+val* var_t /* var t: nullable Object */;
+val* var2 /* : HashSet[nullable Object] */;
+val* var4 /* : HashSet[nullable Object] */;
 short int var5 /* : Bool */;
-/* Covariant cast for argument 0 (t) <p0:Object> isa E */
-/* <p0:Object> isa E */
-type_struct = self->type->resolution_table->types[COLOR_poset__POSetElement_FT0];
+/* Covariant cast for argument 0 (t) <p0:nullable Object> isa E */
+/* <p0:nullable Object> isa E */
+type_struct = self->type->resolution_table->types[COLOR_poset__POSetElement___35dE];
 cltype = type_struct->color;
 idtype = type_struct->id;
+is_nullable = type_struct->is_nullable;
+if(p0 == NULL) {
+var1 = is_nullable;
+} else {
 if(cltype >= p0->type->table_size) {
 var1 = 0;
 } else {
 var1 = p0->type->type_table[cltype] == idtype;
 }
+}
 if (unlikely(!var1)) {
 var_class_name = p0 == NULL ? "null" : p0->type->name;
 PRINT_ERROR("Runtime error: Cast failed. Expected `%s`, got `%s`", "E", var_class_name);
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 280);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 448);
 show_backtrace(1);
 }
 var_t = p0;
 {
-{ /* Inline poset#POSetElement#tos (self) on <self:POSetElement[Object]> */
-var4 = self->attrs[COLOR_poset__POSetElement___tos].val; /* _tos on <self:POSetElement[Object]> */
+{ /* Inline poset#POSetElement#tos (self) on <self:POSetElement[nullable Object]> */
+var4 = self->attrs[COLOR_poset__POSetElement___tos].val; /* _tos on <self:POSetElement[nullable Object]> */
 if (unlikely(var4 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _tos");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 245);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 389);
 show_backtrace(1);
 }
 var2 = var4;
@@ -1776,81 +1515,75 @@ RET_LABEL3:(void)0;
 }
 }
 {
-var5 = hash_collection__HashSet__has(var2, var_t);
+var5 = standard___standard__HashSet___standard__abstract_collection__Collection__has(var2, var_t);
 }
 var = var5;
 goto RET_LABEL;
 RET_LABEL:;
 return var;
 }
-/* method poset#POSetElement#<= for (self: Object, Object): Bool */
-short int VIRTUAL_poset__POSetElement___60d_61d(val* self, val* p0) {
-short int var /* : Bool */;
-short int var1 /* : Bool */;
-var1 = poset__POSetElement___60d_61d(self, p0);
-var = var1;
-RET_LABEL:;
-return var;
-}
-/* method poset#POSetElement#< for (self: POSetElement[Object], Object): Bool */
-short int poset__POSetElement___60d(val* self, val* p0) {
+/* method poset#POSetElement#< for (self: POSetElement[nullable Object], nullable Object): Bool */
+short int poset___poset__POSetElement____60d(val* self, val* p0) {
 short int var /* : Bool */;
 short int var1 /* : Bool */;
 int cltype;
 int idtype;
 const struct type* type_struct;
+short int is_nullable;
 const char* var_class_name;
-val* var_t /* var t: Object */;
+val* var_t /* var t: nullable Object */;
 short int var2 /* : Bool */;
-val* var3 /* : Object */;
-val* var5 /* : Object */;
+val* var3 /* : nullable Object */;
+val* var5 /* : nullable Object */;
 short int var6 /* : Bool */;
 short int var7 /* : Bool */;
 short int var_ /* var : Bool */;
-val* var8 /* : HashSet[Object] */;
-val* var10 /* : HashSet[Object] */;
+val* var8 /* : HashSet[nullable Object] */;
+val* var10 /* : HashSet[nullable Object] */;
 short int var11 /* : Bool */;
-/* Covariant cast for argument 0 (t) <p0:Object> isa E */
-/* <p0:Object> isa E */
-type_struct = self->type->resolution_table->types[COLOR_poset__POSetElement_FT0];
+/* Covariant cast for argument 0 (t) <p0:nullable Object> isa E */
+/* <p0:nullable Object> isa E */
+type_struct = self->type->resolution_table->types[COLOR_poset__POSetElement___35dE];
 cltype = type_struct->color;
 idtype = type_struct->id;
+is_nullable = type_struct->is_nullable;
+if(p0 == NULL) {
+var1 = is_nullable;
+} else {
 if(cltype >= p0->type->table_size) {
 var1 = 0;
 } else {
 var1 = p0->type->type_table[cltype] == idtype;
 }
+}
 if (unlikely(!var1)) {
 var_class_name = p0 == NULL ? "null" : p0->type->name;
 PRINT_ERROR("Runtime error: Cast failed. Expected `%s`, got `%s`", "E", var_class_name);
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 286);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 463);
 show_backtrace(1);
 }
 var_t = p0;
 {
-{ /* Inline poset#POSetElement#element (self) on <self:POSetElement[Object]> */
-var5 = self->attrs[COLOR_poset__POSetElement___element].val; /* _element on <self:POSetElement[Object]> */
-if (unlikely(var5 == NULL)) {
-PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _element");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 242);
-show_backtrace(1);
-}
+{ /* Inline poset#POSetElement#element (self) on <self:POSetElement[nullable Object]> */
+var5 = self->attrs[COLOR_poset__POSetElement___element].val; /* _element on <self:POSetElement[nullable Object]> */
 var3 = var5;
 RET_LABEL4:(void)0;
 }
 }
-{
-var7 = ((short int (*)(val*, val*))(var_t->class->vft[COLOR_kernel__Object___33d_61d]))(var_t, var3) /* != on <var_t:Object>*/;
+if (var_t == NULL) {
+var6 = (var3 != NULL);
+} else {
+var7 = ((short int (*)(val* self, val* p0))(var_t->class->vft[COLOR_standard__kernel__Object___33d_61d]))(var_t, var3) /* != on <var_t:nullable Object>*/;
 var6 = var7;
 }
 var_ = var6;
 if (var6){
 {
-{ /* Inline poset#POSetElement#tos (self) on <self:POSetElement[Object]> */
-var10 = self->attrs[COLOR_poset__POSetElement___tos].val; /* _tos on <self:POSetElement[Object]> */
+{ /* Inline poset#POSetElement#tos (self) on <self:POSetElement[nullable Object]> */
+var10 = self->attrs[COLOR_poset__POSetElement___tos].val; /* _tos on <self:POSetElement[nullable Object]> */
 if (unlikely(var10 == NULL)) {
 PRINT_ERROR("Runtime error: %s", "Uninitialized attribute _tos");
-PRINT_ERROR(" (%s:%d)\n", "../lib/poset.nit", 245);
+PRINT_ERROR(" (%s:%d)\n", FILE_poset, 389);
 show_backtrace(1);
 }
 var8 = var10;
@@ -1858,7 +1591,7 @@ RET_LABEL9:(void)0;
 }
 }
 {
-var11 = hash_collection__HashSet__has(var8, var_t);
+var11 = standard___standard__HashSet___standard__abstract_collection__Collection__has(var8, var_t);
 }
 var2 = var11;
 } else {
@@ -1869,29 +1602,10 @@ goto RET_LABEL;
 RET_LABEL:;
 return var;
 }
-/* method poset#POSetElement#< for (self: Object, Object): Bool */
-short int VIRTUAL_poset__POSetElement___60d(val* self, val* p0) {
-short int var /* : Bool */;
-short int var1 /* : Bool */;
-var1 = poset__POSetElement___60d(self, p0);
-var = var1;
-RET_LABEL:;
-return var;
-}
-/* method poset#POSetElement#init for (self: POSetElement[Object]) */
-void poset__POSetElement__init(val* self) {
+/* method poset#POSetElement#init for (self: POSetElement[nullable Object]) */
+void poset___poset__POSetElement___standard__kernel__Object__init(val* self) {
 {
-((void (*)(val*))(self->class->vft[COLOR_poset__POSetElement__init]))(self) /* init on <self:POSetElement[Object]>*/;
-}
-RET_LABEL:;
-}
-/* method poset#POSetElement#init for (self: Object) */
-void VIRTUAL_poset__POSetElement__init(val* self) {
-{ /* Inline poset#POSetElement#init (self) on <self:Object(POSetElement[Object])> */
-{
-((void (*)(val*))(self->class->vft[COLOR_poset__POSetElement__init]))(self) /* init on <self:Object(POSetElement[Object])>*/;
-}
-RET_LABEL1:(void)0;
+((void (*)(val* self))(self->class->vft[COLOR_poset___poset__POSetElement___standard__kernel__Object__init]))(self) /* init on <self:POSetElement[nullable Object]>*/;
 }
 RET_LABEL:;
 }