fact: Definition singletonSequence {X} (A : X) : Sequence X := (1 ,, λ _, A).
imports: UniMath.Foundations.Sets UniMath.MoreFoundations.Tactics UniMath.MoreFoundations.Subtypes UniMath.Combinatorics.FiniteSequences UniMath.Foundations.NaturalNumbers UniMath.Tactics.EnsureStructuredProofs