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 UnitStep

 http://functions.wolfram.com/14.01.21.0004.01

 Input Form

 Integrate[UnitStep[t] UnitStep[x - t], {t, -Infinity, Infinity}] == x UnitStep[x]

 Standard Form

 Cell[BoxData[RowBox[List[RowBox[List[SubsuperscriptBox["\[Integral]", RowBox[List["-", "\[Infinity]"]], "\[Infinity]"], RowBox[List[RowBox[List[RowBox[List["UnitStep", "[", "t", "]"]], " ", RowBox[List["UnitStep", "[", RowBox[List["x", "-", "t"]], "]"]]]], RowBox[List["\[DifferentialD]", "t"]]]]]], "\[Equal]", RowBox[List["x", " ", RowBox[List["UnitStep", "[", "x", "]"]]]]]]]]

 MathML Form

 - θ UnitStep ( t ) θ UnitStep ( x - t ) t x θ UnitStep ( x ) t -1 UnitStep t UnitStep x -1 t x UnitStep x [/itex]

 Rule Form

 Cell[BoxData[RowBox[List[RowBox[List["HoldPattern", "[", RowBox[List[SubsuperscriptBox["\[Integral]", RowBox[List["-", "\[Infinity]"]], "\[Infinity]"], RowBox[List[RowBox[List[RowBox[List["UnitStep", "[", "t_", "]"]], " ", RowBox[List["UnitStep", "[", RowBox[List["x_", "-", "t_"]], "]"]]]], RowBox[List["\[DifferentialD]", "t_"]]]]]], "]"]], "\[RuleDelayed]", RowBox[List["x", " ", RowBox[List["UnitStep", "[", "x", "]"]]]]]]]]

 Date Added to functions.wolfram.com (modification date)

 2007-05-02