proposition: Lemma pleq_trans x y z : [pcm x <= y] -> [pcm y <= z] -> [pcm x <= z].
proof: Proof. by case=>a -> [b ->]; exists (a \+ b); rewrite joinA. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq bigop fintype finset) pcm(options axioms prelude seqperm pred seqext)