proposition: Lemma dsubeK x y : y \is a fin_num -> x - y + y = x.
proof: Proof. by move=> fy; rewrite !dual_addeE oppeK subeK ?oppeK; case: y fy. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap) mathcomp(mathcomp_extra) signed