public class Operator

{

/**

* Add two natural numbers

* @param a is a NaturalNumber

* @param b is a NaturalNumber

* @return an instance of a class NaturalNumber which is the result of adding a and b

*

*/

public static NaturalNumber add(NaturalNumber a, NaturalNumber b)

{

return null ;

}

/**

* Subtract two natural numbers

* @param a is a NaturalNumber

* @param b is a NaturalNumber

* @return if a is larger than b, return an instance of a class NaturalNumber

* which is the result of subtracting b from a.

* otherwise return an instance of class NaturalNumber with 0

*

*/

public static NaturalNumber subtract(NaturalNumber a, NaturalNumber b)

{

return null ;

}

}