proposition: Lemma validRA (x y z : U) : valid (x \+ (y \+ z)) -> valid (x \+ y \+ z).
proof: Proof. by rewrite joinA. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq bigop fintype finset) pcm(options axioms prelude seqperm pred seqext)