Lemma hzeqeissi {i i0 : hz} (e : hzeq i i0) (e' : hzeq i (i0 + 1 + 1)) : empty. Proof. cbn in e. rewrite e in e'. apply (hzeqissi e'). Qed.
Require Import UniMath.MoreFoundations.PartA. Require Import UniMath.Algebra.Monoids. Require Import UniMath.Algebra.Groups.