Sum[KroneckerDelta[k, n] Subscript[a, k], {k, -Infinity, Infinity}] == Subscript[a, n]

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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> <munderover> <mo> &#8721; </mo> <mrow> <mi> k </mi> <mo> = </mo> <mrow> <mo> - </mo> <mi> &#8734; </mi> </mrow> </mrow> <mi> &#8734; </mi> </munderover> <mrow> <msub> <semantics> <mi> &#948; </mi> <annotation-xml encoding='MathML-Content'> <ci> KroneckerDelta </ci> </annotation-xml> </semantics> <mrow> <mi> k </mi> <mo> , </mo> <mi> n </mi> </mrow> </msub> <mo> &#8290; </mo> <msub> <mi> a </mi> <mi> k </mi> </msub> </mrow> </mrow> <mo> &#63449; </mo> <msub> <mi> a </mi> <mi> n </mi> </msub> </mrow> <annotation-xml encoding='MathML-Content'> <apply> <eq /> <apply> <sum /> <bvar> <ci> k </ci> </bvar> <lowlimit> <apply> <times /> <cn type='integer'> -1 </cn> <infinity /> </apply> </lowlimit> <uplimit> <infinity /> </uplimit> <apply> <times /> <apply> <ci> KroneckerDelta </ci> <ci> k </ci> <ci> n </ci> </apply> <apply> <ci> Subscript </ci> <ci> a </ci> <ci> k </ci> </apply> </apply> </apply> <apply> <ci> Subscript </ci> <ci> a </ci> <ci> n </ci> </apply> </apply> </annotation-xml> </semantics> </math>

Cell[BoxData[RowBox[List[RowBox[List["HoldPattern", "[", RowBox[List[UnderoverscriptBox["\[Sum]", RowBox[List["k_", "=", RowBox[List["-", "\[Infinity]"]]]], "\[Infinity]"], RowBox[List[RowBox[List["KroneckerDelta", "[", RowBox[List["k_", ",", "n_"]], "]"]], " ", SubscriptBox["a_", "k_"]]]]], "]"]], "\[RuleDelayed]", SubscriptBox["aa", "n"]]]]]

2007-05-02