Lemma el_vcons_tl {n} (v : vec A n) (x : A) (i : ⟦ n ⟧) : el (x ::: v) (dni_firstelement i) = el v i. Proof. apply idpath. Defined.
Require Import UniMath.Combinatorics.StandardFiniteSets. Require Import UniMath.Foundations.NaturalNumbers.