proposition: Lemma addRC x y : x + y == y + x.
proof: Proof. exact: (Real.add_commutative R). Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div order) mathcomp(ssralg ssrnum ssrint rat intdiv) Coq(Morphisms Setoid) fourcolor(real realsyntax)