Formatting of right hand side of equation should be identical to formatting of left hand side
<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mfrac>
    <mn>1</mn>
    <mn>42</mn>
  </mfrac>
  <mo>=</mo>
  <mfrac linethickness="1">
    <mn>1</mn>
    <mn>42</mn>
  </mfrac>
</math>
Author: George Chavchanidze, Opera Software ASA