Proposition composable_pairs_rel_comm {C : category} (PB : Pullbacks C) {x : C} (R : internal_relation x) : composable_pairs_rel_src PB R · internal_relation_tar R = composable_pairs_rel_tar PB R · internal_relation_src R. Proof. exact (!(PullbackSqrCommutes _)). Qed.
Require Import UniMath.Foundations.All. Require Import UniMath.MoreFoundations.All. Require Import UniMath.CategoryTheory.Core.Prelude. Require Import UniMath.CategoryTheory.Limits.Pullbacks. Require Import UniMath.CategoryTheory.Limits.Coequalizers. Require Import UniMath.CategoryTheory.RegularAndExact.RegularCategory.