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$\sum _x^0=\underset{x}{\overset{0}{\sum }}=\underset{x}{\overset{0}{\sum }}={\displaystyle \sum _x^0=\underset{x}{\overset{0}{\sum }}=\underset{x}{\overset{0}{\sum }}}$

Source Code:

    <math> 
      <mrow> 
        <munderover> 
          <mo>&#x02211;</mo> 
          <mi>x</mi> 
          <mn>0</mn> 
        </munderover> 
        <mo>=</mo> 
        <munderover> 
          <mo movablelimits='true'>&#x02211; 
          </mo> 
          <mi>x</mi> 
          <mn>0</mn> 
        </munderover> 
        <mo>=</mo> 
        <munderover> 
          <mo movablelimits='false'>&#x02211; 
          </mo> 
          <mi>x</mi> 
          <mn>0</mn> 
        </munderover> 
        <mo>=</mo> 
        <mstyle displaystyle='true'> 
          <munderover> 
            <mo>&#x02211;</mo> 
            <mi>x</mi> 
            <mn>0</mn> 
          </munderover> 
          <mo>=</mo> 
          <munderover> 
            <mo movablelimits='true'>&#x02211; 
            </mo> 
            <mi>x</mi> 
            <mn>0</mn> 
          </munderover> 
          <mo>=</mo> 
          <munderover> 
            <mo movablelimits='false'>&#x02211; 
            </mo> 
            <mi>x</mi> 
            <mn>0</mn> 
          </munderover> 
        </mstyle> 
      </mrow> 
    </math>