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