proposition: Lemma dualelement_2x {n : nat} (i : ⟦ n ⟧%stn) : dualelement (dualelement i) = i.
proof: 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.
imports: UniMath.Foundations.All UniMath.MoreFoundations.All UniMath.Combinatorics.Maybe UniMath.Combinatorics.StandardFiniteSets UniMath.Algebra.Domains_and_Fields UniMath.Algebra.RigsAndRings