<?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>