proposition: Lemma umfiltC p1 p2 f : um_filter p1 (um_filter p2 f) = um_filter p2 (um_filter p1 f).
proof: Proof. by rewrite -!umfilt_predI; apply: eq_in_umfiltE=>x /=; rewrite andbC. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)