proposition: Lemma sumbntg_val : sumbntg = PI ^ 2 / 8.
proof: Proof. apply Rmult_eq_reg_l with 2. replace (2 * (PI ^ 2 / 8)) with (PI ^ 2 / 4) by field. apply (Rseq_cv_unique _ _ _ Sum_bnz Bn_cv). assert(0 < 2) by lra; auto with *. Qed.
imports: Reals Lra Rsequence_facts Rseries Rsequence_subsequence Rtactic Lia ZArith