<?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>