proposition: Lemma ArcTan_zero : ArcTan [0][=][0].
proof: Proof. assert (Z:Dom Tang [0]). apply Tang_Domain'. split; auto with *. stepl (ArcTan (Tan _ Z)). apply ArcTan_Tan; auto with *. apply pfwdef. apply Tan_zero. Qed.
imports: CoRN.transc.InvTrigonom CoRN.tactics.CornTac