from typing import List


def inBothLists(L: List[int], M: List[int]) -> List[int]:
    """Returns a list of unique elements that are present in both L and M."""
    return list({x for x in L if x in M})


def testInBothLists():
    print("Testing inBothLists()...", end="")
    assert inBothLists([1, 2, 3], [3, 2, 4]) == [2, 3]
    assert inBothLists([3, 2, 1], [4, 1, 2, 1]) == [1, 2]
    assert inBothLists([3, 2, 1, 2], [2, 2, 2]) == [2]
    assert inBothLists([1, 2, 3], [4, 5, 6, 1]) == [1]
    assert inBothLists([3, 2, 1, 2], [4]) == []

    # Verify that the function is nonmutating:
    L = [1, 2, 3]
    M = [3, 2, 4]
    inBothLists(L, M)
    assert L == [1, 2, 3] and M == [3, 2, 4]
    print("Passed!")


def main():
    testInBothLists()


main()