[sage-devel] submodules subvectorspaces violate the unique parent condition. Why? Should we change that?

[Simon Brandhorst]

{{{
sage: V = span(QQ,[(1,1),(1,0)])
sage: W = span(QQ,[(0,1),(1,0)])
sage: V

Vector space of degree 2 and dimension 2 over Rational Field
Basis matrix:
[1 0]
[0 1]
sage: W

Vector space of degree 2 and dimension 2 over Rational Field
Basis matrix:
[1 0]
[0 1]
sage: V is W
False
sage: V==W
True
sage: type(V)
<class 'sage.modules.free_module.FreeModule_submodule_field_with_category'>
sage: type(W)
<class 'sage.modules.free_module.FreeModule_submodule_field_with_category'>
}}}

They are parents. Yet they are not unique.

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