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   http://functions.wolfram.com/01.16.27.1991.01
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    ArcCot[(z - 1)/(z + 1)] == I ArcTanh[I z] + 
   (Pi/4) (1 - 2 Sqrt[1 + I z] Sqrt[1/(1 + I z)] + 
     (1 + Sqrt[z^2]/z) (1 - ((1 - z^2)/z) Sqrt[z^2/(-1 + z^2)^2])) /; 
 Abs[z] != 1 
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   Cell[BoxData[RowBox[List[RowBox[List[RowBox[List["ArcCot", "[", FractionBox[RowBox[List["z", "-", "1"]], RowBox[List["z", "+", "1"]]], "]"]], "\[Equal]", RowBox[List[RowBox[List["\[ImaginaryI]", " ", RowBox[List["ArcTanh", "[", RowBox[List["\[ImaginaryI]", " ", "z"]], "]"]]]], "+", RowBox[List[FractionBox["\[Pi]", "4"], RowBox[List["(", RowBox[List["1", "-", RowBox[List["2", " ", SqrtBox[RowBox[List["1", "+", RowBox[List["\[ImaginaryI]", " ", "z"]]]]], " ", SqrtBox[FractionBox["1", RowBox[List["1", "+", RowBox[List["\[ImaginaryI]", " ", "z"]]]]]]]], "+", RowBox[List[RowBox[List["(", RowBox[List["1", "+", FractionBox[SqrtBox[SuperscriptBox["z", "2"]], "z"]]], ")"]], " ", RowBox[List["(", RowBox[List["1", "-", RowBox[List[FractionBox[RowBox[List["1", "-", SuperscriptBox["z", "2"]]], "z"], " ", SqrtBox[FractionBox[SuperscriptBox["z", "2"], SuperscriptBox[RowBox[List["(", RowBox[List[RowBox[List["-", "1"]], "+", SuperscriptBox["z", "2"]]], ")"]], "2"]]]]]]], ")"]]]]]], ")"]]]]]]]], "/;", RowBox[List[RowBox[List["Abs", "[", "z", "]"]], "\[NotEqual]", "1"]]]]]] 
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   <math xmlns='http://www.w3.org/1998/Math/MathML' mathematica:form='TraditionalForm' xmlns:mathematica='http://www.wolfram.com/XML/'>  <semantics>  <mrow>  <mrow>  <mrow>  <msup>  <mi> cot </mi>  <mrow>  <mo> - </mo>  <mn> 1 </mn>  </mrow>  </msup>  <mo> ( </mo>  <mfrac>  <mrow>  <mi> z </mi>  <mo> - </mo>  <mn> 1 </mn>  </mrow>  <mrow>  <mi> z </mi>  <mo> + </mo>  <mn> 1 </mn>  </mrow>  </mfrac>  <mo> ) </mo>  </mrow>  <mo> ⩵ </mo>  <mrow>  <mrow>  <mfrac>  <mi> π </mi>  <mn> 4 </mn>  </mfrac>  <mo> ⁢ </mo>  <mrow>  <mo> ( </mo>  <mrow>  <mrow>  <mrow>  <mo> ( </mo>  <mrow>  <mfrac>  <msqrt>  <msup>  <mi> z </mi>  <mn> 2 </mn>  </msup>  </msqrt>  <mi> z </mi>  </mfrac>  <mo> + </mo>  <mn> 1 </mn>  </mrow>  <mo> ) </mo>  </mrow>  <mo> ⁢ </mo>  <mrow>  <mo> ( </mo>  <mrow>  <mrow>  <mrow>  <mo> - </mo>  <mfrac>  <mrow>  <mn> 1 </mn>  <mo> - </mo>  <msup>  <mi> z </mi>  <mn> 2 </mn>  </msup>  </mrow>  <mi> z </mi>  </mfrac>  </mrow>  <mo> ⁢ </mo>  <msqrt>  <mfrac>  <msup>  <mi> z </mi>  <mn> 2 </mn>  </msup>  <msup>  <mrow>  <mo> ( </mo>  <mrow>  <msup>  <mi> z </mi>  <mn> 2 </mn>  </msup>  <mo> - </mo>  <mn> 1 </mn>  </mrow>  <mo> ) </mo>  </mrow>  <mn> 2 </mn>  </msup>  </mfrac>  </msqrt>  </mrow>  <mo> + </mo>  <mn> 1 </mn>  </mrow>  <mo> ) </mo>  </mrow>  </mrow>  <mo> - </mo>  <mrow>  <mn> 2 </mn>  <mo> ⁢ </mo>  <msqrt>  <mrow>  <mn> 1 </mn>  <mo> + </mo>  <mrow>  <mi> ⅈ </mi>  <mo> ⁢ </mo>  <mi> z </mi>  </mrow>  </mrow>  </msqrt>  <mo> ⁢ </mo>  <msqrt>  <mfrac>  <mn> 1 </mn>  <mrow>  <mn> 1 </mn>  <mo> + </mo>  <mrow>  <mi> ⅈ </mi>  <mo> ⁢ </mo>  <mi> z </mi>  </mrow>  </mrow>  </mfrac>  </msqrt>  </mrow>  <mo> + </mo>  <mn> 1 </mn>  </mrow>  <mo> ) </mo>  </mrow>  </mrow>  <mo> + </mo>  <mrow>  <mi> ⅈ </mi>  <mo> ⁢ </mo>  <mrow>  <msup>  <mi> tanh </mi>  <mrow>  <mo> - </mo>  <mn> 1 </mn>  </mrow>  </msup>  <mo> ( </mo>  <mrow>  <mi> ⅈ </mi>  <mo> ⁢ </mo>  <mi> z </mi>  </mrow>  <mo> ) </mo>  </mrow>  </mrow>  </mrow>  </mrow>  <mo> /; 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  | Cell[BoxData[RowBox[List[RowBox[List["HoldPattern", "[", RowBox[List["ArcCot", "[", FractionBox[RowBox[List["z_", "-", "1"]], RowBox[List["z_", "+", "1"]]], "]"]], "]"]], "\[RuleDelayed]", RowBox[List[RowBox[List[RowBox[List["\[ImaginaryI]", " ", RowBox[List["ArcTanh", "[", RowBox[List["\[ImaginaryI]", " ", "z"]], "]"]]]], "+", RowBox[List[FractionBox["1", "4"], " ", "\[Pi]", " ", RowBox[List["(", RowBox[List["1", "-", RowBox[List["2", " ", SqrtBox[RowBox[List["1", "+", RowBox[List["\[ImaginaryI]", " ", "z"]]]]], " ", SqrtBox[FractionBox["1", RowBox[List["1", "+", RowBox[List["\[ImaginaryI]", " ", "z"]]]]]]]], "+", RowBox[List[RowBox[List["(", RowBox[List["1", "+", FractionBox[SqrtBox[SuperscriptBox["z", "2"]], "z"]]], ")"]], " ", RowBox[List["(", RowBox[List["1", "-", FractionBox[RowBox[List[RowBox[List["(", RowBox[List["1", "-", SuperscriptBox["z", "2"]]], ")"]], " ", SqrtBox[FractionBox[SuperscriptBox["z", "2"], SuperscriptBox[RowBox[List["(", RowBox[List[RowBox[List["-", "1"]], "+", SuperscriptBox["z", "2"]]], ")"]], "2"]]]]], "z"]]], ")"]]]]]], ")"]]]]]], "/;", RowBox[List[RowBox[List["Abs", "[", "z", "]"]], "\[NotEqual]", "1"]]]]]]]]  |  
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   Date Added to functions.wolfram.com (modification date)
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