<?xml version="1.0" encoding="UTF-8"?>
<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
   <semantics xmlns="">
      <mrow>
         <mstyle mathvariant="bold">
            <mi mathvariant="bold">s</mi>
         </mstyle>
      </mrow>
      <annotation encoding="application/x-tex">\boldsymbol{s}</annotation>
   </semantics>
</math>
