proposition: Lemma Rminus_plus_distr : forall r1 r2 r3, r1 - (r2 + r3) = (r1 - r2) - r3.
proof: Proof. now unfold Rminus; intros r1 r2 r3; rewrite Ropp_plus_distr, Rplus_assoc. Qed.
imports: RelationClasses Raxioms Rpow_def ZArith ZArithRing RealField