def METHOD_NAME():
    #   < xx  >  Imagine the intervals x and y as bit strings.
    # | <yy yy>  The bit at position n is set if n falls inside that interval.
    # = <zzzzz>  In this model _union_intervals() performs bit-wise or.
    assert _union_intervals([[2, 3]], [[1, 2], [4, 5]]) == ((1, 5),)