The two specialization hierarchy are symmetric.
redef type MPROPDEF: MAttributeDef
src/model/model.nit:2472,2--35
redef type MPROPDEF: MVirtualTypeDef
src/model/model.nit:2495,2--37
redef type MPROPDEF: MInnerClassDef
src/doc/model_ext.nit:95,2--36
redef type MPROPDEF: MMethodDef
src/model/model.nit:2415,2--32