(C D : PreCategory) : functor C D o functor D C = 1 := idpath.
Require Import HoTT.Basics HoTT.Types. Require Import Category.Core Functor.Core InitialTerminalCategory.Core InitialTerminalCategory.Functors Category.Prod Functor.Prod Functor.Composition.Core Functor.Identity Functor.Composition.Laws.