proposition: Lemma subdom_validL x y a : valid a -> valid (x \+ y) -> {subset dom a <= dom x} -> valid (a \+ y).
proof: Proof. rewrite !validUnAE=>-> /and3P [_ -> D] S. by apply: sub_all D=>z /(contra (S z)). Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)