Lemma dni_first {n : nat} (i: ⟦n⟧ ) : pr1 (dni firstelement i) = S i. Proof. intros. apply idpath. Defined.
Require Import UniMath.MoreFoundations.Tactics. Require Import UniMath.MoreFoundations.DecidablePropositions. Require Import UniMath.MoreFoundations.NegativePropositions.