proposition: Lemma eqR_trans x y z : x == y -> y == z -> x == z.
proof: Proof. by case=> lexy leyx [leyz lezy]; split=> a; auto. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq order) mathcomp(ssralg ssrnum ssrint rat) fourcolor(real) Coq(Setoid Morphisms)