<html xmlns="http://www.w3.org/1999/xhtml">
  <div>
    <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline">
      <notin>
        <mspace>
          <mfenced />
        </mspace>

        f
      </notin>
    </math>
  </div>
</html>