Proposition two_of_six_is_prop {C : category} (W : morph_class C) : isaprop (two_of_six W). Proof. unfold two_of_six. repeat (apply impred ; intro). apply isofhleveltotal2. apply (W _ _ _). intro. apply isofhleveltotal2. apply (W _ _ _). intro. apply isofhleveltotal2. apply (W _ _ _). intro. apply (W _ _ _). Defined.
Require Import UniMath.Foundations.All. Require Import UniMath.MoreFoundations.All. Require Import UniMath.CategoryTheory.Monics. Require Import UniMath.CategoryTheory.Epis. Require Import UniMath.CategoryTheory.Core.Categories. Require Import UniMath.CategoryTheory.Core.Functors. Require Import UniMath.CategoryTheory.Core.Isos.