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