proposition: Lemma adde_defC x y : x +? y = y +? x.
proof: Proof. by rewrite /adde_def andbC (andbC (x == -oo)) (andbC (x == +oo)). Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap) mathcomp(mathcomp_extra) signed