@sig(H/ ("a"/ H >> "a" >> bool) >> ["a"] >> ["a"] >> ["a"])
def unionBy(f, xs, ys):
    """
    unionBy :: (a -> a -> Bool) -> [a] -> [a] -> [a]

    The unionBy function is the non-overloaded version of union.
    """
    raise NotImplementedError()
dataset/ETHPy150Open billpmurphy/hask/hask/Data/List.py/unionBy/swapped operands of `/`