proposition: Lemma sin_lt_0_var : forall x:R, - PI < x -> x < 0 -> sin x < 0.
proof: Proof. intros; generalize (Rplus_lt_compat_l (2 * PI) (- PI) x H); replace (2 * PI + - PI) with PI; [ intro H1; rewrite Rplus_comm in H1; generalize (Rplus_lt_compat_l (2 * PI) x 0 H0); intro H2; rewrite (Rplus_comm (2 * PI)) in H2; rewrite <- (Rplus_comm 0) in H2; rewrite Rplus_0_l in H2; rewrite <- (sin_period x 1); unfold INR in |- *; replace (2 * 1 * PI) with (2 * PI); [ apply (sin_lt_0 (x + 2 * PI) H1 H2) | ring ] | ring ]. Qed.
imports: Rbase Rfunctions SeqSeries Rtrigo_fun Rtrigo_def Rtrigo_alt Cos_rel Cos_plus ZArith_base Zcomplements Lia Lra Ranalysis1 Rsqrt_def PSeries_reg