def test_is_cnf():
    (x, y, z) = symbols('x,y,z')
    assert (is_cnf(((x | y) | z)) == True)
    assert (is_cnf(((x & y) & z)) == True)
    assert (is_cnf(((x | y) & z)) == True)
    assert (is_cnf(((x & y) | z)) == False)
def test_is_cnf():
    (x, y, z) = symbols('x,y,z')
    assert (is_cnf(((x | y) | z)) == True)
    assert (is_cnf(((x & y) & z)) == True)
    assert (is_cnf(((x | y) & z)) == True)
    assert (is_cnf(((x & y) | z)) == False)