proposition: Lemma addKR x y : - x + (x + y) == y.
proof: Proof. by rewrite addRCA addRA subRR add0R. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div order) mathcomp(ssralg ssrnum ssrint rat intdiv) Coq(Morphisms Setoid) fourcolor(real realsyntax)