mml=<math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced open="{" close="}"><mrow><mn>3</mn><mo>-</mo><mfenced><mrow><mn>4</mn><mo>-</mo><mover><mrow><mn>2</mn><mo>-</mo><mn>3</mn></mrow><mo>¯</mo></mover></mrow></mfenced></mrow></mfenced></math>