mml=<math xmlns="http://www.w3.org/1998/Math/MathML"><mstyle mathsize="12px"><mfenced open="{" close="}" separators="|"><mfrac><mrow><mi mathvariant="normal">r</mi><mfenced separators="|"><mrow><mi mathvariant="normal">r</mi><mo>-</mo><mn>1</mn></mrow></mfenced></mrow><mrow><mn>2</mn><mi mathvariant="normal">x</mi></mrow></mfrac></mfenced></mstyle></math>