Definition:Functor/Contravariant/Definition 1
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Definition
Let $\mathbf C$ and $\mathbf D$ be metacategories.
A contravariant functor $F : \mathbf C \to \mathbf D$ consists of:
- An object functor $F_0$ that assigns to each object $X$ of $\mathbf C$ an object $FX$ of $\mathbf D$.
- An arrow functor $F_1$ that assigns to each arrow $f : X \to Y$ of $\mathbf C$ an arrow $Ff : FY \to FX$ of $\mathbf D$.
These functors must satisfy, for any morphisms $X \stackrel f \longrightarrow Y \stackrel g \longrightarrow Z$ in $\mathbf C$:
- $\map F {g \circ f} = F f \circ F g$
and:
- $\map F {\operatorname {id}_X} = \operatorname {id}_{F X}$
where:
- $\operatorname {id}_W$ denotes the identity arrow on an object $W$
and:
- $\circ$ is the composition of morphisms.
Also see
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