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