def compare_lists(firstlist, secondlist):
    """
    Takes two lists and compares them
    Returns a set of common fields and two lists of differences in a tuple
    """
    common = set(firstlist).intersection(secondlist)
    first_difference = [item for item in firstlist if item not in common]
    second_difference = [item for item in secondlist if item not in common]
    return (common, first_difference, second_difference)