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# 2-functor

In mathematics, specifically, in category theory, a 2-functor is a morphism between 2-categories.[1] They may be defined formally using enrichment by saying that a 2-category is exactly a Cat-enriched category and a 2-functor is a Cat-functor.[2]

Explicitly, if C and D are 2-categories then a 2-functor ${\displaystyle F\colon C\to D}$ consists of

• a function ${\displaystyle F\colon {\text{Ob}}C\to {\text{Ob}}D}$, and
• for each pair of objects ${\displaystyle c,c'\in {\text{Ob}}C}$, a functor ${\displaystyle F_{c,c'}\colon {\text{Hom}}_{C}(c,c')\to {\text{Hom}}_{D}(Fc,Fc')}$

such that each ${\displaystyle F_{c,c'}}$ strictly preserves identity objects and they commute with horizontal composition in C and D.

See [3] for more details and for lax versions.

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• Category Theory 6.2: Functors in programming
• Highest common functor and list common multiple