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In category theory, a branch of mathematics, a presheaf on a category is a functor . If is the poset of open sets in a topological space, interpreted as a category, then one recovers the usual notion of presheaf on a topological space. A morphism of presheaves is defined to be a natural transformation of functors. This makes the collection of all presheaves into a category, and is an example of a functor category. It is often written as is sometimes called a profunctor. A presheaf that is naturally isomorphic to the contravariant hom-functor Hom(–,''A'') for some object ''A'' of C is called a representable presheaf. Some authors refer to a functor as a -valued presheaf. == Examples == * A simplicial set is a Set-valued presheaf on the simplex category . 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Presheaf (category theory)」の詳細全文を読む スポンサード リンク
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