proposition: Lemma addRK x y : x + y - y == x.
proof: Proof. by rewrite -addRA subRR addR0. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div order) mathcomp(ssralg ssrnum ssrint rat intdiv) Coq(Morphisms Setoid) fourcolor(real realsyntax)