data/mathtoweb/53.mml
<math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>E</mi><mrow><mo rspace="0.3em" lspace="0em" stretchy="true" fence="true" form="prefix">[</mo><msup><mrow><mover accent="true"><mi>σ</mi><mo>^</mo></mover></mrow><mn>2</mn></msup><mo rspace="0em" lspace="0.3em" stretchy="true" fence="true" form="postfix">]</mo></mrow><mo>=</mo><mfrac linethickness="1"><mrow><mi>n</mi><mo>-</mo><mn>1</mn></mrow><mi>n</mi></mfrac><msup><mi>σ</mi><mn>2</mn></msup></mrow></math>