//  Mass class 
//  -----------

#ifndef MASS
#define MASS const Mass
class Force;                      //  Interacting  
class Acceleration;               //    classes 

 class Mass {

   double value;                  //   Grams

 public:
  
//  Constructors and accessors
//  --------------------------

  Mass(DOUBLE x=0) : value(x) {}

//  The compiler will provide an acceptable copy constructor,
//  destructor, and assignment operator.

  double grams()   const {return value;}

//  Operations on Mass operands

#define  Class Mass
#include "Additive.hpp"
  bool operator==(MASS rs) const {return value == rs.value;}
  bool operator< (MASS rs) const {return value  < rs.value;}

//  Arithmetic operations on mixed operands (Newton's law)

    Force operator* (const Acceleration rs) const;  //  Newton's law
   

};                          //  *****  End of class definition


 ostream& operator<<(ostream& ls, MASS rs); // Output stream insertion
    

#undef Class
#endif