fst o (a * b) = a. Proof. path_functor; trivial. Defined.
Require Import Category.Core Functor.Core Category.Prod Functor.Composition.Core Functor.Prod.Core. Require Import Functor.Paths. Require Import Types.Prod HoTT.Tactics Types.Forall Types.Sigma. Require Import Basics.Tactics.