rec-arg1

arg(x+iy)

<math xmlns="http://www.w3.org/1998/Math/MathML">
  <apply>
    <csymbol cd="complex1">argument</csymbol>
    <apply>
      <csymbol cd="arith1">plus</csymbol>
      <ci>x</ci>
      <apply>
        <csymbol cd="arith1">times</csymbol>
        <csymbol cd="nums1">i</csymbol>
        <ci>y</ci>
      </apply>
    </apply>
  </apply>
</math>

Author: MathML 2 Recommendation