Objects¶

class
sage.categories.objects.
Objects
(s=None)¶ Bases:
sage.categories.category_singleton.Category_singleton
The category of all objects the basic category
EXAMPLES:
sage: Objects() Category of objects sage: Objects().super_categories() []

class
ParentMethods
¶ Bases:
object
Methods for all category objects

class
SubcategoryMethods
¶ Bases:
object

Endsets
()¶ Return the category of endsets between objects of this category.
EXAMPLES:
sage: Sets().Endsets() Category of endsets of sets sage: Rings().Endsets() Category of endsets of unital magmas and additive unital additive magmas
See also

Homsets
()¶ Return the category of homsets between objects of this category.
EXAMPLES:
sage: Sets().Homsets() Category of homsets of sets sage: Rings().Homsets() Category of homsets of unital magmas and additive unital additive magmas
Note
Background
Information, code, documentation, and tests about the category of homsets of a category
Cs
should go in the nested classCs.Homsets
. They will then be made available to homsets of any subcategory ofCs
.Assume, for example, that homsets of
Cs
areCs
themselves. This information can be implemented in the methodCs.Homsets.extra_super_categories
to makeCs.Homsets()
a subcategory ofCs()
.Methods about the homsets themselves should go in the nested class
Cs.Homsets.ParentMethods
.Methods about the morphisms can go in the nested class
Cs.Homsets.ElementMethods
. However it’s generally preferable to put them in the nested classCs.MorphimMethods
; indeed they will then apply to morphisms of all subcategories ofCs
, and not only full subcategories.See also
FunctorialConstruction
Todo
 Design a mechanism to specify that an axiom is
compatible with taking subsets. Examples:
Finite
,Associative
,Commutative
(when meaningful), but notInfinite
norUnital
.  Design a mechanism to specify that, when \(B\) is a subcategory of \(A\), a \(B\)homset is a subset of the corresponding \(A\) homset. And use it to recover all the relevant axioms from homsets in super categories.
 For instances of redundant code due to this missing
feature, see:
AdditiveMonoids.Homsets.extra_super_categories()
HomsetsCategory.extra_super_categories()
(slightly different nature) plus plenty of spots where this is not implemented.
 Design a mechanism to specify that an axiom is
compatible with taking subsets. Examples:


additional_structure
()¶ Return
None
Indeed, by convention, the category of objects defines no additional structure.
See also
EXAMPLES:
sage: Objects().additional_structure()

super_categories
()¶ EXAMPLES:
sage: Objects().super_categories() []

class