proposition: Lemma umcnt_umfiltC p q f : um_count p (um_filter q f) = um_count q (um_filter p f).
proof: Proof. by rewrite !umcnt_umfilt; apply: eq_in_umcnt=>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)