x is unknown, T=True, F=False, ttt = x or x or x, otherwise all connected with "and" By definition: #1: xTTTTT #2: xxFFFF #3: TTxxxx #4: tttxxx #5:

x is unknown, T=True, F=False, ttt = x or x or x, otherwise all connected with "and" By definition: #1: xTTTTT #2: xxFFFF #3: TTxxxx #4: tttxxx #5: FFFFxx #6: FFFFFx Begin evaluation from 6. Let's assume 6 is T so we have xxxxxT. In that case 5 need to be F. But if 5 is F, then any from [1,2,3,4] need to be T. But if any from [1,2,3,4] is T then 6 cannot be T. Thus 6 cannot be T, so it is F if correct answer exists. Now we have: xxxxxF Next, we try to set 5 to T: xxxxTF. 1 cannot be T, 2 cannot be T, since their last elements are different (TT!=TF, FF!=TF), 3 cannot be T because it requires 1 and 2 be both T , 4 cannot be T because (1 or 2 or 3) are F. So we have: FFFFTF Thus only 5 is True.