In a monoidal category $(C, \otimes, I)$, the **unit object** (or *tensor unit*) $I$ is the object which plays the role of the unit for the tensor product $\otimes$, in that for any other object $a$ there are isomorphisms $a \otimes I \simeq a$ and $I \otimes a \simeq a$ (the unitors).

Dually, in a closed category there is a *unit object* which is such that maps out of it into an internal hom correspond to the external hom.

Last revised on October 11, 2023 at 08:08:59. See the history of this page for a list of all contributions to it.