Proposition cha_not_not_not {H : complete_heyting_algebra} (x : H) : ¬ ¬ ¬ x = ¬ x. Proof. use cha_le_antisymm. - use cha_to_le_exp. refine (cha_le_trans _ _). { refine (cha_and_monotone_r _). apply cha_not_not. } use cha_exp_eval. - apply cha_not_not. Qed.
Require Import UniMath.MoreFoundations.All. Require Import UniMath.Algebra.BinaryOperations. Require Import UniMath.OrderTheory.Lattice.Lattice. Require Import UniMath.OrderTheory.Lattice.Bounded. Require Import UniMath.OrderTheory.Lattice.Heyting. Require Import UniMath.OrderTheory.Lattice.CompleteHeyting.