Definition opp_retraction : retraction (A : C^opp) (B : C^opp) := retraction_retraction r ,, retraction_section r ,, retraction_is_retraction r.
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.