proposition: Lemma Some_fnd V (f : {fmap K -> V}) (k : domf f) : Some (f k) = f.[? val k].
proof: Proof. by case: fndP (valP k) => // ? _; rewrite getfE. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop)