<math xmlns='http://www.w3c.org/mathml' version='2.0'>
  <apply> <eq/>
    <apply> <diff/> 
      <bvar> <ci> x </ci> </bvar> 
      <apply> <times/> 
        <ci> a </ci> 
        <ci> u </ci> 
      </apply>
    </apply>
    <apply> <times/>
      <ci> a </ci>
      <apply> <diff/> 
        <bvar> <ci> x </ci> </bvar> 
        <ci> u </ci>
      </apply>
    </apply>
  </apply>
</math>