proposition: Lemma validUUn k v f1 f2 : k \in dom f1 -> valid (upd k v f1 \+ f2) = valid (f1 \+ f2).
proof: Proof. by move=>D; rewrite -!(joinC f2); apply: validUnU D. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)