Lemma isaset_retraction (A B : ob C) (H : has_homsets C) : isaset (retraction A B). Proof. do 2 (apply isaset_total2; [apply H | intro]). apply isasetaprop. apply isaprop_is_retraction. apply H. Qed.
Require Import UniMath.Foundations.All. Require Import UniMath.MoreFoundations.All. Require Import UniMath.CategoryTheory.Core.Categories. Require Import UniMath.CategoryTheory.Core.Functors. Require Import UniMath.CategoryTheory.OppositeCategory.Core.