
<!DOCTYPE math
  PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<math xmlns="http://www.w3.org/1998/Math/MathML">
<apply><partialdiff/>
 <bvar><ci> x </ci></bvar>
 <bvar><ci> y </ci></bvar>
 <apply><ci type="fn"> f </ci>
  <ci> x </ci>
  <ci> y </ci>
 </apply>
</apply>
</math>