Isomorphic Objects Functorial Construction#

AUTHORS:

Nicolas M. Thiery (2010): initial revision

class sage.categories.isomorphic_objects.IsomorphicObjectsCategory(category, *args)#

Bases: sage.categories.covariant_functorial_construction.RegressiveCovariantConstructionCategory

classmethod default_super_categories(category)#

Returns the default super categories of category.IsomorphicObjects()

Mathematical meaning: if $A$ is the image of $B$ by an isomorphism in the category $C$ , then $A$ is both a subobject of $B$ and a quotient of $B$ in the category $C$ .

INPUT:

cls – the class IsomorphicObjectsCategory

category – a category $C a t$

OUTPUT: a (join) category

In practice, this returns category.Subobjects() and category.Quotients(), joined together with the result of the method RegressiveCovariantConstructionCategory.default_super_categories() (that is the join of category and cat.IsomorphicObjects() for each cat in the super categories of category).

EXAMPLES:

Consider category=Groups(), which has cat=Monoids() as super category. Then, the image of a group $G^{'}$ by a group isomorphism is simultaneously a subgroup of $G$ , a subquotient of $G$ , a group by itself, and the image of $G$ by a monoid isomorphism:

sage: Groups().IsomorphicObjects().super_categories()
[Category of groups,
 Category of subquotients of monoids,
 Category of quotients of semigroups,
 Category of isomorphic objects of sets]

Mind the last item above: there is indeed currently nothing implemented about isomorphic objects of monoids.

This resulted from the following call:

sage: sage.categories.isomorphic_objects.IsomorphicObjectsCategory.default_super_categories(Groups())
Join of Category of groups and
Category of subquotients of monoids and
Category of quotients of semigroups and
Category of isomorphic objects of sets