Definition functor_op {C D : category} (F : functor C D) : functor (opp_cat C) (opp_cat D) := functor_opp F.
Require Import UniMath.Foundations.All. Require Import UniMath.CategoryTheory.Core.Categories. Require Import UniMath.CategoryTheory.Core.Functors. Require Import UniMath.CategoryTheory.opp_precat.