Lemma stn_right_first (n i : nat) : stn_right i (S n) firstelement = make_stn (i + S n) i (natltplusS n i). Proof. intros. apply subtypePath_prop. simpl. apply natplusr0. Defined.
Require Import UniMath.MoreFoundations.Tactics. Require Import UniMath.MoreFoundations.DecidablePropositions. Require Import UniMath.MoreFoundations.NegativePropositions.