rec-fn3

(f+g)(z)

<math xmlns="http://www.w3.org/1998/Math/MathML">
  <apply>
    <apply>
      <csymbol cd="arith1">plus</csymbol>
      <ci>f</ci>
      <ci>g</ci>
    </apply>
    <ci>z</ci>
  </apply>
</math>

Author: MathML 2 Recomendation