proposition: Lemma In_umfiltX p x f : x \In f -> p x -> x \In um_filter p f.
proof: Proof. by move=>X1 X2; apply/In_umfilt. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)