Proposition cha_not_not {H : complete_heyting_algebra} (x : H) : x ≤ ¬ ¬ x. Proof. use cha_to_le_exp. rewrite cha_min_comm. use cha_exp_eval. 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.