Bicategory
= Bicategory
{wiki}
A bicategory has objects, hom-categories, composition functors and identity 1-cells. Associativity and unit laws hold through coherent invertible 2-cells, satisfying pentagon and triangle identities. A <monoidal category> is exactly a bicategory with a single object: its objects are the 1-cells, its morphisms the 2-cells, and its tensor product the horizontal composition.