proposition: Lemma _PI2_RLT_0 : - (PI / 2) < 0.
proof: Proof. assert (H := PI_RGT_0). lra. 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