proposition: Lemma addeK x y : x \is a fin_num -> y + x - x = y.
proof: Proof. by move: x y => [x| |] [y| |] //; rewrite -EFinD -EFinB addrK. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap) mathcomp(mathcomp_extra) signed