proposition: Lemma mule_def_fin x y : x \is a fin_num -> y \is a fin_num -> x *? y.
proof: Proof. move: x y => [x| |] [y| |] finx finy//. by rewrite /mule_def negb_or 2!negb_and/= 2!orbT. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap) mathcomp(mathcomp_extra) signed