def is_trivial(four_cycle):
    """
    A trivial four cycle in the dual graph bounds a single quadrilateral
    """
    crossings = map(lambda x: map(lambda y: y.crossing, x.interface),
        four_cycle)
    return len(set(crossings[0]) & set(crossings[1]) & set(crossings[2]) &
        set(crossings[3])) != 0
