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