<?xml version="1.0" encoding="UTF-8"?>

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">  <munderover>    <mrow>      <munderover>        <mi mathvariant="normal">BASE</mi>         <mi mathvariant="normal">under-1</mi>         <mphantom>          <mi mathvariant="normal">fail</mi>
        </mphantom>       </munderover>     </mrow>     <mi mathvariant="normal">under-2</mi>     <mphantom>      <mi mathvariant="normal">fail</mi>
    </mphantom>   </munderover>   <mo>=</mo>   <munder>    <mrow>      <munder>        <mi mathvariant="normal">BASE</mi>         <mi mathvariant="normal">under-1</mi>       </munder>     </mrow>     <mi mathvariant="normal">under-2</mi>   </munder> </math>