text: // -i operators.in operators.hh --
  class Op {
  public:
      Op operator+() const;
      Op operator-() const;
      Op& operator*();
  
      Op operator+(const Op &o) const;
      Op operator-(const Op &o) const;
      Op operator*(double d) const;
      Op operator/(const Op &o) const;
  
      Op& operator +=(const Op &o);
      Op& operator -=(double d);
      Op& operator *=(double d);
      Op& operator /=(double d);
  
      bool operator<(double d);
      bool operator<=(double d);
      bool operator>(const Op &o);
      bool operator>=(const Op &o);
      bool operator==(double d);
      bool operator!=(const Op &o);
  
      friend Op operator*(double d, const Op &);
  };
  