proposition: Lemma cexit3 h1 h : empty = h1 -> h = h :+ h1.
proof: Proof. by move=><-; rewrite unh0. Qed.
imports: mathcomp(ssreflect ssrfun ssrnat div ssrbool seq) LemmaOverloading(prelude finmap ordtype) mathcomp(path eqtype) Eqdep