Definition dni_firstelement {n : nat} : ⟦n⟧ -> ⟦S n⟧. Proof. intros h. exact (S (pr1 h),, pr2 h). Defined.
Require Import UniMath.MoreFoundations.Tactics. Require Import UniMath.MoreFoundations.DecidablePropositions. Require Import UniMath.MoreFoundations.NegativePropositions.