def __new__(cls, function, *symbols, **assumptions):
        obj = AddWithLimits.__new__(cls, function, *symbols, **assumptions)
        if not hasattr(obj, 'limits'):
            return obj
        if any(len(l) != 3 or None in l for l in obj.limits):
            raise ValueError('Sum requires values for lower and upper bounds.')

        return obj

    def __new__(cls, function, *symbols, **assumptions):
        """Create an unevaluated integral.

        Arguments are an integrand followed by one or more limits.

        If no limits are given and there is only one free symbol in the
        expression, that symbol will be used, otherwise an error will be
        raised.

        >>> from sympy import Integral
        >>> from sympy.abc import x, y
        >>> Integral(x)
        Integral(x, x)
        >>> Integral(y)
        Integral(y, y)

        When limits are provided, they are interpreted as follows (using
        ``x`` as though it were the variable of integration):

            (x,) or x - indefinite integral
            (x, a) - "evaluate at" integral is an abstract antiderivative
            (x, a, b) - definite integral

        The ``as_dummy`` method can be used to see which symbols cannot be
        targeted by subs: those with a preppended underscore cannot be
        changed with ``subs``. (Also, the integration variables themselves --
        the first element of a limit -- can never be changed by subs.)

        >>> i = Integral(x, x)
        >>> at = Integral(x, (x, x))
        >>> i.as_dummy()
        Integral(x, x)
        >>> at.as_dummy()
        Integral(_x, (_x, x))

        """

        #This will help other classes define their own definitions
        #of behaviour with Integral.
        if hasattr(function, '_eval_Integral'):
            return function._eval_Integral(*symbols, **assumptions)

        obj = AddWithLimits.__new__(cls, function, *symbols, **assumptions)
        return obj