<?xml version="1.0" encoding="UTF-8"?>

<math xmlns="http://www.w3.org/1998/Math/MathML">
  <mfenced>
    <mrow>
      <mi>a</mi> 
      <mo>+</mo> 
      <mi>b</mi> 
    </mrow> 
  </mfenced> 
  <mo>+</mo> 
  <mfenced>
    <mfrac>
      <mn>1</mn> 
      <mn>2</mn> 
    </mfrac> 
  </mfenced> </math>