Lemma cancel_precomposition (C : precategory_data) (a b c: C) (f f' : b --> c) (g : a --> b) : f = f' -> g · f = g · f'. Proof. apply maponpaths. Defined.
Require Import UniMath.Foundations.Propositions. Require Import UniMath.Foundations.Sets. Require Import UniMath.MoreFoundations.PartA. Require Import UniMath.MoreFoundations.Notations.