(** ** Derivative of arcsine *)

(* Specifications: *)
Lemma derivable_pt_asin : forall x, -1 < x < 1 ->
derivable_pt asin x.
Lemma derive_pt_asin : forall (x : R) (Hxrange : -1 < x < 1),
derive_pt asin x (derivable_pt_asin x Hxrange) = 1 / sqrt (1 - x²).