proposition: Lemma In_cond f x : x \In f -> C x.1.
proof: Proof. by move/In_dom/dom_cond. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)