The notion of a cocartesian coclosed category is dual to that of a cartesian closed category.
A cocartesian coclosed category is a category with finite coproducts and coexponential objects.
Any category which is both cartesian closed and cocartesian coclosed is a thin category, though it may not be the terminal category (e.g., any Boolean algebra is such a category).
Let a category be given which is both cartesian closed and cocartesian coclosed. Cartesian closure tells us that the product of any object with the initial object will be itself initial (as left adjoints preserve colimits). Furthermore, given any morphism from an object to , we can pair this with the identity morphism on to obtain a morphism from into with a left inverse given by projection, thus identifying as a retract of an initial object, and therefore as an initial object itself. It follows immediately that any two parallel morphisms to are equal; equivalently, by the dual reasoning, any two parallel morphisms out of are equal. But this means any two parallel morphisms in general are equal, as maps from to can be identified with maps from to ; accordingly, the category must be a thin category.
The Kleisli category of a continuation monad on a cartesian closed category with coproduct is cocartesian coclosed. In fact , which we can prove using the cartesian closure of :
Last revised on June 8, 2024 at 18:38:48. See the history of this page for a list of all contributions to it.