proposition: Lemma Rmult_eq_reg_l : forall r r1 r2, r * r1 = r * r2 -> r <> 0 -> r1 = r2.
proof: Proof. intros r r1 r2 H r_not_0. apply (Rmult_eq_compat_l (/ r)) in H. now rewrite <-2Rmult_assoc, Rinv_l, 2Rmult_1_l in H. Qed.
imports: RelationClasses Raxioms Rpow_def ZArith ZArithRing RealField