plus3

-1 + 7

<math xmlns="http://www.w3.org/1998/Math/MathML">
  <apply>
    <csymbol cd="arith1">plus</csymbol>
    <apply>
      <csymbol cd="arith1">unary_minus</csymbol>
      <cn>1</cn>
    </apply>
    <cn>7</cn>
  </apply>
</math>

Author: Design Science, Inc. (E. Cannon, E. Tabacman, R.Miner)