proposition: Lemma find_some k v f : find k f = Some v -> k \in dom f.
proof: Proof. by 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)