Opened 5 years ago

#21160 new enhancement

the default implementation of Homset.identity is wrong

Reported by: vdelecroix Owned by:
Priority: major Milestone: sage-7.3
Component: categories Keywords:
Cc: nthiery, SimonKing Merged in:
Authors: Reviewers:
Report Upstream: N/A Work issues:
Branch: Commit:
Dependencies: Stopgaps:

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Description

The method sage.categories.Homset.identity should not try to bypass the _element_constructor_... as a consequence of the current behavior

sage: R.<x,y> = QQ[]
sage: A = AffineSpace(R)
sage: Ai = A.Hom(A).identity()
sage: f = A.Hom(A)([1,2])
sage: f * Ai
Traceback (most recent call last):
...
TypeError: right (=Identity endomorphism of Affine Space of dimension 2 over Rational Field) must be a SchemeMorphism to multiply it by Scheme endomorphism of Affine Space of dimension 2 over Rational Field
  Defn: Defined on coordinates by sending (x, y) to
        (1, 2)

(Vincent): I think that this IdentityMorphism should just not exist. There is no such thing as OneElement and ZeroElement that is spoiled all over Sage for the zero and one of algebraic structures...

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