boost-react-native-bundle/boost_1_57_0/libs/math/doc/equations/error2.mml

Boost library as in https://sourceforge.net/projects/boost/files/boost/1.57.0/

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mrow>
    <mo>|</mo>
    <mfrac>
      <mrow>
        <mi>a</mi>
        <mo>&#x2212;</mo>
        <mi>v</mi>
      </mrow>
      <mi>a</mi>
    </mfrac>
    <mo>|</mo>
  </mrow>
</math>