Definition slice_counit : slice_to_PreShv ∙ PreShv_to_slice ⟹ functor_identity (PreShv C / P) := slice_counit_fun ,, is_nat_trans_slice_counit.
Require Import UniMath.Foundations.Sets. Require Import UniMath.MoreFoundations.Tactics. Require Import UniMath.CategoryTheory.Core.Categories. Require Import UniMath.CategoryTheory.Core.Isos. Require Import UniMath.CategoryTheory.Core.Functors. Require Import UniMath.CategoryTheory.Core.NaturalTransformations. Require Import UniMath.CategoryTheory.FunctorCategory. Require Import