<document source="test data">
    <paragraph>
        Einstein derived the famous equation
    <paragraph>
        <math title="E=mc^2" xmlns="&mathml;" label="einstein"><mstyle displaystyle="true"><mi>E</mi><mo>=</mo><mi>m</mi><msup><mi>c</mi><mn>2</mn></msup></mstyle></math>
        <substitution_definition names="einstein">
            1
    <paragraph>
        As you can see in equation 
        <substitution_reference refname="einstein">
            einstein
        , a little mass converts to a
        large amount of energy.