proposition: Lemma xsep_validL a b : xsep_valid (xsep_join a b) -> xsep_valid a.
proof: Proof. rewrite /xsep_valid/xsep_join !unlock /= /xsep_join'. case: ifP; last by rewrite tpcmE. by case/andP=>W E; rewrite !(validE2 W) (sepx0 W E). Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(eqtype fintype) pcm(options axioms prelude) pcm(pcm)