Proposition double_id_mor_id {C : category} {D : twosided_disp_cat C C} (I : hor_id D) (x : C) : double_id_mor I (identity x) = id_two_disp _. Proof. exact (pr12 I x). Defined.
Require Import UniMath.Foundations.All. Require Import UniMath.MoreFoundations.All. Require Import UniMath.CategoryTheory.Core.Categories. Require Import UniMath.CategoryTheory.Core.Isos. Require Import UniMath.CategoryTheory.TwoSidedDisplayedCats.TwoSidedDispCat. Require Import UniMath.CategoryTheory.TwoSidedDisplayedCats.Isos.