<math xmlns="http://www.w3.org/1998/Math/MathML">
  <semantics>
    <mrow>
      <mi>f</mi>
      <mo>&ApplyFunction;</mo>
      <mfenced close=")" open="(">
        <mi>x</mi>
      </mfenced>
    </mrow>
    <annotation-xml encoding="MathML-Content">
      <apply>
        <ci type="function">f</ci>
        <ci>x</ci>
      </apply>
    </annotation-xml>
    <annotation encoding="SnuggleTeX">$f(x)$</annotation>
    <annotation encoding="LaTeX">$f(x)$</annotation>
    <annotation encoding="Maxima">f(x)</annotation>
  </semantics>
</math>

<math xmlns="http://www.w3.org/1998/Math/MathML">
  <semantics>
    <mrow>
      <mi>f</mi>
      <mfenced close=")" open="(">
        <mi>x</mi>
      </mfenced>
    </mrow>
    <annotation encoding="SnuggleTeX">$f(x)$</annotation>
  </semantics>
</math>

<math xmlns="http://www.w3.org/1998/Math/MathML">
  <mrow>
    <mi>f</mi>
    <mo>&ApplyFunction;</mo>
    <mfenced close=")" open="(">
      <mi>x</mi>
    </mfenced>
  </mrow>
</math>

<math xmlns="http://www.w3.org/1998/Math/MathML">
  <apply>
    <ci type="function">f</ci>
    <ci>x</ci>
  </apply>
</math>

f(x)