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   http://functions.wolfram.com/04.03.27.0003.01
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    Round[z] == IntegerPart[z + (1 + I)/2] - 1 - I - 
  I CharacteristicFunction[(1/4) (-1 + 2 Im[z]), Integers] - 
  CharacteristicFunction[(1/4) (-1 + 2 Re[z]), Integers] + 
  I Sign[CharacteristicFunction[1/2 + Im[z], Integers] + 
     UnitStep[1/2 + Im[z]]] + 
  Sign[CharacteristicFunction[1/2 + Re[z], Integers] + UnitStep[1/2 + Re[z]]] 
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   Cell[BoxData[RowBox[List[RowBox[List["Round", "[", "z", "]"]], "\[Equal]", RowBox[List[RowBox[List["IntegerPart", "[", RowBox[List["z", "+", FractionBox[RowBox[List["1", "+", "\[ImaginaryI]"]], "2"]]], "]"]], "-", "1", "-", "\[ImaginaryI]", "-", RowBox[List["\[ImaginaryI]", " ", RowBox[List["CharacteristicFunction", "[", RowBox[List[RowBox[List[FractionBox["1", "4"], " ", RowBox[List["(", RowBox[List[RowBox[List["-", "1"]], "+", RowBox[List["2", " ", RowBox[List["Im", "[", "z", "]"]]]]]], ")"]]]], ",", "Integers"]], "]"]]]], "-", RowBox[List["CharacteristicFunction", "[", RowBox[List[RowBox[List[FractionBox["1", "4"], " ", RowBox[List["(", RowBox[List[RowBox[List["-", "1"]], "+", RowBox[List["2", " ", RowBox[List["Re", "[", "z", "]"]]]]]], ")"]]]], ",", "Integers"]], "]"]], "+", RowBox[List["\[ImaginaryI]", " ", RowBox[List["Sign", "[", RowBox[List[RowBox[List["CharacteristicFunction", "[", RowBox[List[RowBox[List[FractionBox["1", "2"], "+", RowBox[List["Im", "[", "z", "]"]]]], ",", "Integers"]], "]"]], "+", RowBox[List["UnitStep", "[", RowBox[List[FractionBox["1", "2"], "+", RowBox[List["Im", "[", "z", "]"]]]], "]"]]]], "]"]]]], "+", RowBox[List["Sign", "[", RowBox[List[RowBox[List["CharacteristicFunction", "[", RowBox[List[RowBox[List[FractionBox["1", "2"], "+", RowBox[List["Re", "[", "z", "]"]]]], ",", "Integers"]], "]"]], "+", RowBox[List["UnitStep", "[", RowBox[List[FractionBox["1", "2"], "+", RowBox[List["Re", "[", "z", "]"]]]], "]"]]]], "]"]]]]]]]] 
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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>  <mo> ⌊ </mo>  <mi> z </mi>  <mo> ⌉ </mo>  </mrow>  <mo> ⩵ </mo>  <mrow>  <mrow>  <mi> int </mi>  <mo> ⁡ </mo>  <mo> ( </mo>  <mrow>  <mi> z </mi>  <mo> + </mo>  <mfrac>  <mrow>  <mn> 1 </mn>  <mo> + </mo>  <mi> ⅈ </mi>  </mrow>  <mn> 2 </mn>  </mfrac>  </mrow>  <mo> ) </mo>  </mrow>  <mo> - </mo>  <mn> 1 </mn>  <mo> - </mo>  <mi> ⅈ </mi>  <mo> - </mo>  <mrow>  <msub>  <mi> χ </mi>  <mi> ℤ </mi>  </msub>  <mo> ( </mo>  <mfrac>  <mrow>  <mrow>  <mn> 2 </mn>  <mo> ⁢ </mo>  <mrow>  <mi> Re </mi>  <mo> ⁡ </mo>  <mo> ( </mo>  <mi> z </mi>  <mo> ) </mo>  </mrow>  </mrow>  <mo> - </mo>  <mn> 1 </mn>  </mrow>  <mn> 4 </mn>  </mfrac>  <mo> ) </mo>  </mrow>  <mo> - </mo>  <mrow>  <mi> ⅈ </mi>  <mo> ⁢ </mo>  <mrow>  <msub>  <mi> χ </mi>  <mi> ℤ </mi>  </msub>  <mo> ( </mo>  <mfrac>  <mrow>  <mrow>  <mn> 2 </mn>  <mo> ⁢ </mo>  <mrow>  <mi> Im </mi>  <mo> ⁡ </mo>  <mo> ( </mo>  <mi> z </mi>  <mo> ) </mo>  </mrow>  </mrow>  <mo> - </mo>  <mn> 1 </mn>  </mrow>  <mn> 4 </mn>  </mfrac>  <mo> ) </mo>  </mrow>  </mrow>  <mo> + </mo>  <mrow>  <mi> sgn </mi>  <mo> ⁡ </mo>  <mo> ( </mo>  <mrow>  <mrow>  <msub>  <mi> χ </mi>  <mi> ℤ </mi>  </msub>  <mo> ( </mo>  <mrow>  <mrow>  <mi> Re </mi>  <mo> ⁡ </mo>  <mo> ( </mo>  <mi> z </mi>  <mo> ) </mo>  </mrow>  <mo> + </mo>  <mfrac>  <mn> 1 </mn>  <mn> 2 </mn>  </mfrac>  </mrow>  <mo> ) </mo>  </mrow>  <mo> + </mo>  <mrow>  <mi> θ </mi>  <mo> ⁡ </mo>  <mo> ( </mo>  <mrow>  <mrow>  <mi> Re </mi>  <mo> ⁡ </mo>  <mo> ( </mo>  <mi> z </mi>  <mo> ) </mo>  </mrow>  <mo> + </mo>  <mfrac>  <mn> 1 </mn>  <mn> 2 </mn>  </mfrac>  </mrow>  <mo> ) </mo>  </mrow>  </mrow>  <mo> ) </mo>  </mrow>  <mo> + </mo>  <mrow>  <mi> ⅈ </mi>  <mo> ⁢ </mo>  <mrow>  <mi> sgn </mi>  <mo> ⁡ </mo>  <mo> ( </mo>  <mrow>  <mrow>  <msub>  <mi> χ </mi>  <mi> ℤ </mi>  </msub>  <mo> ( </mo>  <mrow>  <mrow>  <mi> Im </mi>  <mo> ⁡ </mo>  <mo> ( </mo>  <mi> z </mi>  <mo> ) </mo>  </mrow>  <mo> + </mo>  <mfrac>  <mn> 1 </mn>  <mn> 2 </mn>  </mfrac>  </mrow>  <mo> ) </mo>  </mrow>  <mo> + </mo>  <mrow>  <mi> θ </mi>  <mo> ⁡ </mo>  <mo> ( </mo>  <mrow>  <mrow>  <mi> Im </mi>  <mo> ⁡ </mo>  <mo> ( </mo>  <mi> z </mi>  <mo> ) </mo>  </mrow>  <mo> + </mo>  <mfrac>  <mn> 1 </mn>  <mn> 2 </mn>  </mfrac>  </mrow>  <mo> ) </mo>  </mrow>  </mrow>  <mo> ) </mo>  </mrow>  </mrow>  </mrow>  </mrow>  <annotation-xml encoding='MathML-Content'>  <apply>  <ci> FormBox </ci>  <apply>  <ci> ErrorBox </ci>  <apply>  <ci> RowBox </ci>  <list>  <ms> ⌊z⌉ </ms>  <ms> ⩵ </ms>  <apply>  <ci> RowBox </ci>  <list>  <apply>  <ci> RowBox </ci>  <list>  <ms> int </ms>  <ms> ( </ms>  <apply>  <ci> RowBox </ci>  <list>  <ms> z </ms>  <ms> + </ms>  <apply>  <ci> FractionBox </ci>  <apply>  <ci> RowBox </ci>  <list>  <ms> 1 </ms>  <ms> + </ms>  <ms> ⅈ </ms>  </list>  </apply>  <ms> 2 </ms>  </apply>  </list>  </apply>  <ms> ) </ms>  </list>  </apply>  <ms> - </ms>  <ms> 1 </ms>  <ms> - </ms>  <ms> ⅈ </ms>  <ms> - </ms>  <apply>  <ci> RowBox </ci>  <list>  <apply>  <ci> SubscriptBox </ci>  <ms> χ </ms>  <ms> ℤ </ms>  </apply>  <ms> ( </ms>  <apply>  <ci> FractionBox </ci>  <apply>  <ci> RowBox </ci>  <list>  <apply>  <ci> RowBox </ci>  <list>  <ms> 2 </ms>  <apply>  <ci> RowBox </ci>  <list>  <ms> Re </ms>  <ms> ( </ms>  <ms> z </ms>  <ms> ) </ms>  </list>  </apply>  </list>  </apply>  <ms> - </ms>  <ms> 1 </ms>  </list>  </apply>  <ms> 4 </ms>  </apply>  <ms> ) </ms>  </list>  </apply>  <ms> - </ms>  <apply>  <ci> RowBox </ci>  <list>  <ms> ⅈ </ms>  <apply>  <ci> RowBox </ci>  <list>  <apply>  <ci> SubscriptBox </ci>  <ms> χ </ms>  <ms> ℤ </ms>  </apply>  <ms> ( </ms>  <apply>  <ci> FractionBox </ci>  <apply>  <ci> RowBox </ci>  <list>  <apply>  <ci> RowBox </ci>  <list>  <ms> 2 </ms>  <apply>  <ci> RowBox </ci>  <list>  <ms> Im </ms>  <ms> ( </ms>  <ms> z </ms>  <ms> ) </ms>  </list>  </apply>  </list>  </apply>  <ms> - </ms>  <ms> 1 </ms>  </list>  </apply>  <ms> 4 </ms>  </apply>  <ms> ) </ms>  </list>  </apply>  </list>  </apply>  <ms> + </ms>  <apply>  <ci> RowBox </ci>  <list>  <ms> sgn </ms>  <ms> ( </ms>  <apply>  <ci> RowBox </ci>  <list>  <apply>  <ci> RowBox </ci>  <list>  <apply>  <ci> SubscriptBox </ci>  <ms> χ </ms>  <ms> ℤ </ms>  </apply>  <ms> ( </ms>  <apply>  <ci> RowBox </ci>  <list>  <apply>  <ci> RowBox </ci>  <list>  <ms> Re </ms>  <ms> ( </ms>  <ms> z </ms>  <ms> ) </ms>  </list>  </apply>  <ms> + </ms>  <apply>  <ci> FractionBox </ci>  <ms> 1 </ms>  <ms> 2 </ms>  </apply>  </list>  </apply>  <ms> ) </ms>  </list>  </apply>  <ms> + </ms>  <apply>  <ci> RowBox </ci>  <list>  <ms> θ </ms>  <ms> ( </ms>  <apply>  <ci> RowBox </ci>  <list>  <apply>  <ci> RowBox </ci>  <list>  <ms> Re </ms>  <ms> ( </ms>  <ms> z </ms>  <ms> ) </ms>  </list>  </apply>  <ms> + </ms>  <apply>  <ci> FractionBox </ci>  <ms> 1 </ms>  <ms> 2 </ms>  </apply>  </list>  </apply>  <ms> ) </ms>  </list>  </apply>  </list>  </apply>  <ms> ) </ms>  </list>  </apply>  <ms> + </ms>  <apply>  <ci> RowBox </ci>  <list>  <ms> ⅈ </ms>  <apply>  <ci> RowBox </ci>  <list>  <ms> sgn </ms>  <ms> ( </ms>  <apply>  <ci> RowBox </ci>  <list>  <apply>  <ci> RowBox </ci>  <list>  <apply>  <ci> SubscriptBox </ci>  <ms> χ </ms>  <ms> ℤ </ms>  </apply>  <ms> ( </ms>  <apply>  <ci> RowBox </ci>  <list>  <apply>  <ci> RowBox </ci>  <list>  <ms> Im </ms>  <ms> ( </ms>  <ms> z </ms>  <ms> ) </ms>  </list>  </apply>  <ms> + </ms>  <apply>  <ci> FractionBox </ci>  <ms> 1 </ms>  <ms> 2 </ms>  </apply>  </list>  </apply>  <ms> ) </ms>  </list>  </apply>  <ms> + </ms>  <apply>  <ci> RowBox </ci>  <list>  <ms> θ </ms>  <ms> ( </ms>  <apply>  <ci> RowBox </ci>  <list>  <apply>  <ci> RowBox </ci>  <list>  <ms> Im </ms>  <ms> ( </ms>  <ms> z </ms>  <ms> ) </ms>  </list>  </apply>  <ms> + </ms>  <apply>  <ci> FractionBox </ci>  <ms> 1 </ms>  <ms> 2 </ms>  </apply>  </list>  </apply>  <ms> ) </ms>  </list>  </apply>  </list>  </apply>  <ms> ) </ms>  </list>  </apply>  </list>  </apply>  </list>  </apply>  </list>  </apply>  </apply>  <ci> TraditionalForm </ci>  </apply>  </annotation-xml>  </semantics>  </math> 
   
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  | Cell[BoxData[RowBox[List[RowBox[List["HoldPattern", "[", RowBox[List["Round", "[", "z_", "]"]], "]"]], "\[RuleDelayed]", RowBox[List[RowBox[List["IntegerPart", "[", RowBox[List["z", "+", FractionBox[RowBox[List["1", "+", "\[ImaginaryI]"]], "2"]]], "]"]], "-", "1", "-", "\[ImaginaryI]", "-", RowBox[List["\[ImaginaryI]", " ", RowBox[List["CharacteristicFunction", "[", RowBox[List[RowBox[List[FractionBox["1", "4"], " ", RowBox[List["(", RowBox[List[RowBox[List["-", "1"]], "+", RowBox[List["2", " ", RowBox[List["Im", "[", "z", "]"]]]]]], ")"]]]], ",", "Integers"]], "]"]]]], "-", RowBox[List["CharacteristicFunction", "[", RowBox[List[RowBox[List[FractionBox["1", "4"], " ", RowBox[List["(", RowBox[List[RowBox[List["-", "1"]], "+", RowBox[List["2", " ", RowBox[List["Re", "[", "z", "]"]]]]]], ")"]]]], ",", "Integers"]], "]"]], "+", RowBox[List["\[ImaginaryI]", " ", RowBox[List["Sign", "[", RowBox[List[RowBox[List["CharacteristicFunction", "[", RowBox[List[RowBox[List[FractionBox["1", "2"], "+", RowBox[List["Im", "[", "z", "]"]]]], ",", "Integers"]], "]"]], "+", RowBox[List["UnitStep", "[", RowBox[List[FractionBox["1", "2"], "+", RowBox[List["Im", "[", "z", "]"]]]], "]"]]]], "]"]]]], "+", RowBox[List["Sign", "[", RowBox[List[RowBox[List["CharacteristicFunction", "[", RowBox[List[RowBox[List[FractionBox["1", "2"], "+", RowBox[List["Re", "[", "z", "]"]]]], ",", "Integers"]], "]"]], "+", RowBox[List["UnitStep", "[", RowBox[List[FractionBox["1", "2"], "+", RowBox[List["Re", "[", "z", "]"]]]], "]"]]]], "]"]]]]]]]]  |  
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   Date Added to functions.wolfram.com (modification date)
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