fact: Definition drop_and_append {X n} (x : stn (S n) -> X) : append (n,,x ∘ dni_lastelement) (x lastelement) = (S n,, x).
imports: UniMath.Combinatorics.FiniteSets UniMath.Combinatorics.Lists UniMath.Combinatorics.Vectors UniMath.MoreFoundations.PartA UniMath.MoreFoundations.Tactics