def verification_digit(numbers):
        """
        Returns the verification digit for a given numbre.

        The verification digit is calculated as follows:

        * A = sum of all even-positioned numbers
        * B = A * 3
        * C = sum of all odd-positioned numbers
        * D = B + C
        * The results is the smallset number N, such that (D + N) % 10 == 0

        NOTE: Afip's documentation seems to have odd an even mixed up in the
        explanation, but all examples follow the above algorithm.

        :param list(int) numbers): The numbers for which the digits is to be
            calculated.
        :return: int
        """
        a = sum(numbers[::2])
        b = a * 3
        c = sum(numbers[1::2])
        d = b + c
        e = d % 10
        if e == 0:
            return e
        return 10 - e