proposition: Lemma pleqV (x1 x2 : U) : [pcm x1 <= x2] -> valid x2 -> valid x1.
proof: Proof. by case=>x -> /validL. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq bigop fintype finset) pcm(options axioms prelude seqperm pred seqext)