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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def write_unregistered_file(date=None):
 """ Write .unregistered out to disk """

    delete_registered_file()
    if date is None:
        date = get_time()
    for f in constants.unregistered_files:
        if os.path.lexists(f):
            if os.path.islink(f):
                # kill symlinks and regenerate
                os.remove(f)
                write_to_disk(f, content=str(date))
        else:
            write_to_disk(f, content=str(date))