(*****************************************************************)
(** * Using series definitions of cos and sin                    *)
(*****************************************************************)

Definition sin_lb (a:R) : R := sin_approx a 3.Definition sin_ub (a:R) : R := sin_approx a 4.Definition cos_lb (a:R) : R := cos_approx a 3.Definition cos_ub (a:R) : R := cos_approx a 4.

Lemma tan_increasing_1 : forall x y:R, - (PI / 4) <= x -> x <= PI / 4 -> - (PI / 4) <= y -> y <= PI / 4 -> x < y -> tan x < tan y.