s d (m : morphism ((A -> C)^op * (B -> C)) s d) (x : fst s / snd s) : (fst d / snd d) := CommaCategory.
Require Import Category.Core Functor.Core NaturalTransformation.Core. Require Import Category.Dual. Require Import Category.Prod. Require Import NaturalTransformation.Identity. Require Import FunctorCategory.Core Cat.Core. Require Import InitialTerminalCategory.Core InitialTerminalCategory.Functors. Import Comma.Core. Require Import HoTT.Tactics. Require Import Basics.Tactics.