class REAL:  # nested.py
    def __init__(self, l, u):
        self.lower = l
        self.upper = u

    def asString(self, n):
        l = self.lower(n)
        u = self.upper(n)
        return ("[ " + l.numerator.digits() + "/" + l.denominator.digits() +
                ", " + u.numerator.digits() + "/" + u.denominator.digits() + "]")

    def __add__(self, y):
        return REAL_add(self, y)


class REAL_add(REAL):
    def __init__(self, x, y):
        self.x = x
        self.y = y

    def lower(self, n):
        return self.x.lower(n) + self.y.lower(n)

    def upper(self, n):
        return self.x.upper(n) + self.y.upper(n)