<<< native
[ EIdentifier "x" , ESymbol Bin "+" , EIdentifier "y" ]
>>> omml
<?xml version='1.0' ?>
<m:oMathPara>
  <m:oMathParaPr>
    <m:jc m:val="center" />
  </m:oMathParaPr>
  <m:oMath>
    <m:r>
      <m:t>x</m:t>
    </m:r>
    <m:r>
      <m:rPr>
        <m:sty m:val="p" />
      </m:rPr>
      <m:t>+</m:t>
    </m:r>
    <m:r>
      <m:t>y</m:t>
    </m:r>
  </m:oMath>
</m:oMathPara>