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