def sum_rec_one(x):
    """
    Sums an array using down-by-one recursion.

    @type  x: iterable
    @param x: the array to sum

    @rtype: int
    @return: the sum of all array values
    """
    if len(x) == 0:
        return 0
    return x[0] + sum_rec_one(x[1:])