proposition: Lemma Rlt_mult_neg_neg: forall r1 r2 : R, r1<0 -> r2<0 -> 0 < r1 * r2.
proof: Proof. intros r1 r2 Hr1 Hr2; stepr ((-r1)*(-r2)); [|ring]; apply Rmult_lt_0_compat; lra. Qed.
imports: Coq(Reals) Coq(Lra) Coq(Fourier) Coq(Euclid) Coq(Lia)