Definition. Locally Discrete Bicategory

Every category 𝒞︀ is a bicategory 𝖫𝖣(𝒞︀) with only identity 2-cells. Its 0-cells are the objects of 𝒞︀, and the hom-category 𝖫𝖣(𝒞︀)(𝑥,𝑦) is the discrete category on the set 𝒞︀(𝑥,𝑦): a 2-cell 𝑓⇒𝑔 is a proof that 𝑓=𝑔. Composition and identities are those of 𝒞︀; the unitors and associator are the unit and associativity laws of 𝒞︀. Since the homs of 𝒞︀ are sets, any two parallel 2-cells are equal, so the triangle and pentagon hold trivially.

A functor 𝐹:𝒞︀→𝒟︀ gives a pseudofunctor 𝖫𝖣(𝐹):𝖫𝖣(𝒞︀)→𝖫𝖣(𝒟︀), whose comparison 2-cells are the functor laws of 𝐹.

The locally discrete bicategory is how ordinary indexed categories enter bicategorical language: a prestack on 𝖫𝖣(𝒞︀) is a pseudofunctor 𝒞︀op→𝖢𝖠𝖳, and its Grothendieck construction is a displayed category over 𝒞︀.

locally-discrete-bicategory definition entries/bicategory/locally-discrete-bicategory.hel