
<!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>
  <csymbol encoding="OpenMath" definitionURL="http://www.openmath.org/cd/BesselFunctions.ocd">
    <msub><mi>J</mi><mn>0</mn></msub>
  </csymbol>
  <ci>y</ci>
</apply>


<csymbol encoding="text" definitionURL="www.example.org/universalconstants/Boltzmann.htm">
  k
</csymbol>
</math>