proposition: Lemma ArcTan_one : ArcTan [1][=]Pi[/]FourNZ.
proof: Proof. assert (Z:Dom Tang (Pi[/]FourNZ)). apply Tang_Domain'. split; auto with *. stepl (ArcTan (Tan _ Z)). apply ArcTan_Tan; auto with *. apply pfwdef. apply Tan_QuarterPi. Qed.
imports: CoRN.transc.InvTrigonom CoRN.tactics.CornTac