msubsup-04.mml

<?xml version='1.0' ?>
<math display="block" xmlns="http://www.w3.org/1998/Math/MathML">
  <mrow>
    <msubsup>
      <mi>A</mi>
      <msubsup>
        <mi>C</mi>
        <mn>4</mn>
        <mn>3</mn>
      </msubsup>
      <msubsup>
        <mi>B</mi>
        <mn>2</mn>
        <mn>1</mn>
      </msubsup>
    </msubsup>
    <mo>=</mo>
    <msubsup>
      <mi>A</mi>
      <msubsup>
        <mi>C</mi>
        <msub>
          <mn>4</mn>
          <mphantom>
            <mtext mathvariant="normal">l</mtext>
          </mphantom>
        </msub>
        <mn>3</mn>
      </msubsup>
      <msubsup>
        <mi>B</mi>
        <mn>2</mn>
        <msup>
          <mn>1</mn>
          <mphantom>
            <mtext mathvariant="normal">s</mtext>
          </mphantom>
        </msup>
      </msubsup>
    </msubsup>
  </mrow>
</math>