Lemma dualelement_2x {n : nat} (i : ⟦ n ⟧%stn) : dualelement (dualelement i) = i. Proof. do 2 rewrite dualelement_defs_eq; unfold dualelement'. unfold make_stn. apply subtypePath_prop; simpl. rewrite minusminusmmn; try reflexivity. apply natgthtogehm1, (pr2 i). Defined.
Require Import UniMath.Foundations.All. Require Import UniMath.MoreFoundations.All. Require Import UniMath.Combinatorics.Maybe. Require Import UniMath.Combinatorics.StandardFiniteSets. Require Import UniMath.Algebra.Domains_and_Fields. Require Import UniMath.Algebra.RigsAndRings.