Can't edit. Explanation for 6 is incorrect as pointed above/below. Correct explanation is: Lets say 6 is True. This implies that 5 is False. If 5 is False, it means at least one of the above 5 - 1, 2, 3, 4 is True. But we've established above that all of them are False. So, 5 cannot be False. Hence, 6 cannot be True.