proposition: Lemma transitive_llen: transitive llen.
proof: Proof. by move => x y z /= sa /ltnW sb; exact: (ltn_trans sa sb). Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq path fintype div bigop binomial) mathcomp(prime finset ssralg ssrnum ssrint)