product
<math xmlns="http://www.w3.org/1998/Math/MathML">
<apply>
<product/>
<bvar>
<ci>x</ci>
</bvar>
<condition>
<reln>
<in/>
<ci>x</ci>
<ci type="set">B</ci>
</reln>
</condition>
<apply>
<fn>
<ci>f</ci>
</fn>
<ci>x</ci>
</apply>
</apply>
</math>
Author: Design Science, Inc. (E. Cannon, E. Tabacman, R.Miner)