message: Normalize arithmetic outputs
diff: @@ -218,7 +218,7 @@ struct Plus {
  }
  static std::string description()
  {
  - return "plus";
  + return "+";
  }
  typedef T type;
  };
  @@ -231,7 +231,7 @@ struct Minus {
  }
  static std::string description()
  {
  - return "minus";
  + return "-";
  }
  typedef T type;
  };
  @@ -244,7 +244,7 @@ struct Div {
  }
  static std::string description()
  {
  - return "divided by";
  + return "/";
  }
  typedef T type;
  };
  @@ -257,7 +257,7 @@ struct Mul {
  }
  static std::string description()
  {
  - return "multiplied by";
  + return "*";
  }
  typedef T type;
  };
  @@ -271,7 +271,7 @@ struct Pow {
  }
  static std::string description()
  {
  - return "to the power of";
  + return "^";
  }
  typedef T type;
  };
  @@ -3658,7 +3658,7 @@ public:
  if (m_left) {
  s += m_left->description();
  }
  - s += oper::description();
  + s += (" " + oper::description() + " ");
  if (m_right) {
  s += m_right->description();
  }
  