Definition. Locally Discrete Bicategory
Every category is a bicategory with only identity 2-cells. Its 0-cells are the objects of , and the hom-category is the discrete category on the set : a 2-cell is a proof that . Composition and identities are those of ; the unitors and associator are the unit and associativity laws of . Since the homs of are sets, any two parallel 2-cells are equal, so the triangle and pentagon hold trivially.
A functor gives a pseudofunctor , whose comparison 2-cells are the functor laws of .
The locally discrete bicategory is how ordinary indexed categories enter bicategorical language: a prestack on is a pseudofunctor , and its Grothendieck construction is a displayed category over .