proposition: Lemma In_findNE k f : k \notin dom f -> find k f = None.
proof: Proof. by move/In_findN. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)