(* More efficient way to compute approximations of PI. *)

Lemma PI_2_3_7_ineq :
forall N : nat,
sum_f_R0 (tg_alt PI_2_3_7_tg) (S (2 * N)) <= PI / 4 <=
sum_f_R0 (tg_alt PI_2_3_7_tg) (2 * N).