<?xml version="1.0" encoding="UTF-8"?>
<math xmlns="http://www.w3.org/1998/Math/MathML">
   <mfenced close="}" open="{">
      <msup>
         <mover accent="true">
            <mi>ξ</mi>
            <mo>→</mo>
         </mover>
         <mi>μ</mi>
      </msup>
      <msup>
         <mi>τ</mi>
         <mi>μ</mi>
      </msup>
   </mfenced>
</math>
