class One(object):
    def succ(self, n):
        return n + 1  
    def pred(self, n):
        return n - 1  
    def add(self, n, m):
        if n == 0:
            return m
        else:
            return self.succ(self.add(self.pred(n), m))
            
class Two(One):
    def __init__(self):
        print "An object of type Two was created."
    def mul(self, n, m):
        if n == 0:
            return 0
        elif n == 1:
            return m
        else:
            return self.add(m, self.mul(self.pred(n), m))
            
class Three(Two):
    def __init__(self):
        print "An object of type Three was created."
    def pow(self, n, m):
        if m == 0:
            if n == 0:
                return None
            else:
                return 1
        else:
            return self.mul(n, self.pow(n, self.pred(m)))