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x + 1 + y + x

Source Code:

    <math> 
      <mi>x</mi> 
      <mo>+</mo> 
      <mstyle background='yellow'> 
        <mpadded depth ='-500px'> 
          <mfrac> 
            <mn>1</mn> 
            <mi>&#x0210F;</mi> 
          </mfrac> 
          <mo>+</mo> 
          <mi>y</mi> 
        </mpadded> 
      </mstyle> 
      <mo>+</mo> 
      <mi>x</mi> 
    </math>