assert i != null
v.assign(v.variable(variables.first), i)
else if self.variables.length == 2 then
var key_meth = self.method_key
assert key_meth != null
assert i != null
v.assign(v.variable(variables.first), i)
else if self.variables.length == 2 then
var key_meth = self.method_key
assert key_meth != null