proposition: Lemma cond_find k f : ~~ C k -> find k f = None.
proof: Proof. by move/(cond_dom f); case: dom_find. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)