rec-ci3

x of a

<math xmlns="http://www.w3.org/1998/Math/MathML">
  <semantics>
    <ci>xa-msubmimi</ci>
    <annotation-xml encoding="MathML-Presentation">
      <msub>
        <mi>x</mi>
        <mi>a</mi>
      </msub>
    </annotation-xml>
  </semantics>
</math>

Author: MathML 2 Recommendation