<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>
Author: Robert Miner and Jeff Schaefer, Geometry Technologies