proposition: Lemma pi2_int : 7/8 <= PI2 <= 7/4.
proof: Proof. unfold PI2; case PI_2_aux; simpl; tauto. 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