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