proposition: Lemma valid_umfilt p f : valid (um_filter p f) = valid f.
proof: Proof. by rewrite /um_filter valid_omap. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)