Map (higher-order function)

In mathematics, a category is distributive if it has finite products and finite coproducts such that for every choice of objects $A,B,C$, the canonical map

$[{\mathit{i}\mathit{d}}_A\times {\iota }_1,{\mathit{i}\mathit{d}}_A\times {\iota }_2]:A\times B+A\times C\to A\times (B+C)$

is an isomorphism, and for all objects $A$, the canonical map $0\to A\times 0$ is an isomorphism. Equivalently. if for every object $A$ the functor $A\times -$ preserves coproducts up to isomorphisms $f$. It follows that $f$ and aforementioned canonical maps are equal for each choice of objects.

In particular, if the functor $A\times -$ has a right adjoint (i.e., if the category is cartesian closed), it necessarily preserves all colimits, and thus any cartesian closed category with finite coproducts (i.e., any bicartesian closed category) is distributive.

For example, Set is distributive, while Grp is not, even though it has both products and coproducts.

References

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