proposition: Lemma umfiltUn p f1 f2 : valid (f1 \+ f2) -> um_filter p (f1 \+ f2) = um_filter p f1 \+ um_filter p f2.
proof: Proof. by move=>W; rewrite /um_filter omapUn. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)