// This function computes the sum of x and y
//   using the property:  x+y = (x+1) + (y-1) 
//   and the special case when y=0 (x+y=x)

unsigned int add(unsigned int x, unsigned int y) {
  if (y==0) 
    return(x);
  else
    return(add(x+1,y-1));
}

int main() { 
   add(4,3);
}