mml=<math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mfenced><mfrac><mi mathvariant="normal">a</mi><mi mathvariant="normal">b</mi></mfrac></mfenced><mn>3</mn></msup><mo>-</mo><mfrac><mrow><mn>3</mn><mi mathvariant="normal">a</mi></mrow><msup><mi mathvariant="normal">b</mi><mn>2</mn></msup></mfrac></math>