/*  Interface for operands to RPN Calculator; only implement addition, subtraction, and
 *  multiplication, as division is rather messy for polynomials. Calculator can operate
 *  on any object that satisfies this interface. 
 *  Note that this interface is generic, and needs to be instantiated 
 */ 
public interface CalculatorOperand<T> { 
  
 void addTo (T addend);     // Adds addend to the operand represented by this class
 
 void subtractFrom (T subtrahend);   // Ditto for subtraction
 
 void multiplyBy (T multiplicand);   // Ditto for multiplication
 
 String toString();            // Provide a string representation of this operand suitable for printing
 
}