Logic Puzzle!

You know that one logic puzzle with the labrynth guards? Well this is a copypasta of that with a twist, enjoy.

Three guards stand infront of three doors, one is the exit to the building, if you pick the wrong door you are stabbed, One always tells the truth, one always lies, and the 3rd stabs you if you ask questions more than 7 words long, and if you say more than 3 sentences.  What do?

Does the third guard tell the truth or not?

Walk up to 3rd guard, say "Wat door?" He points, walk out correct door unscathed.

Get on my fuckin level, >>1

"Will 8 word questions get me stabbed?" - 7 words, gets rid of the liar
"Does my question length matter to you?" or "Will you stab me after 3 sentences?" - Indicates which one is the stabber
"Which door is the correct door?" - By process of elimination, I now know who tells the truth so he'll point to the correct door.

>>4
Nice, do you have any good puzzles?

>>2
>>3
The stabbing guard is assumed to be mute

>>6
People who are mute can communicate with sign language and gestures. Like pointing, for example.

>>7
Damn, well then it's fair game

>>5
Wish I did, but I have none off-hand. If I remember any that haven't been spammed to hell on the imageboards I'll add it here because I haven't been on dis in a fucklong time.

All right, try this.

A trial was held to find a spy. The trial had three defendants: A, B and C. One of the defendants was a knight, who always tells the truth, one was a knave, who always lies, and the other was the spy, who can either tell the truth or lie.

During the trial, A either said "C is a knave" or "C is the spy," but we don't know which.
B either said "A is a knight," "A is a knave" or "A is the spy."
C either said "B is a knight," "B is a knave" or "B is the spy."

A logician who makes no mistakes was asked to solve this problem and claimed he did not have enough information. He was then told what exactly A had said and figured out who the spy is.

Who is the spy?

>>10
HURR
I forgot to mention that the judge, who knew each defendant's exact statement, was able to deduce who the spy was. You can't solve this puzzle without knowing that.

>>10
>>11
I'm either stumped or I haven't spent enough time working out out

>>10
Assuming the knight knows who the spy/knave is...

The knight cannot claim anyone else is a knight, so A must be a knight since apparently it is not possible for him to do so.

If he said C is a knave then B is the spy.

If he said C is a spy then C is the spy.

>>13
I never said A was unable to say C was a knight, I just said he didn't. And even if he were, by similar logic, if A were the knave and C the knight, A wouldn't be able to say C was a knight either, so A could also be the knave.

>>14
The knight can only give one answer per person. There are only 2 other people so that's 2 possibilities.

The knave can give 2 answers per person, he can call the spy a knight or a knave and he can call the knight a spy or a knave, that is 3 possibilities.

>>14
The knight can only give one answer per person. There are only 2 other people so that's 2 possibilities.

The knave can give 2 answers per person, he can call the spy a knight or a knave and he can call the knight a spy or a knave, that is 3 possibilities.

>>14
When asked the identity of someone besides themselves...

The knight can only call the spy a spy and the knave a knave. He can only say "spy" or "knave".

The knave can call the spy a knight or a knave and he can call the knight a spy or a knave. He can say "knight", "knave" or "spy".

>>14
When asked the identity of someone besides themselves...

The knight can only call the spy a spy and the knave a knave. He can only say "spy" or "knave".

The knave can call the spy a knight or a knave and he can call the knight a spy or a knave. He can say "knight", "knave" or "spy".

>>15-18
aps, it kept saying "can't post because no subject test"

I hope my multiple explanations make things clear.

>>14
Oh, and lastly, since B and C did say "knight", by deduction they cannot be the knight.

>>15-19
What you are saying is true, but when I say something like "B either said 'A is a knight,' 'A is a knave' or 'A is the spy,'" that's just me giving you incomplete information and has nothing to do with what B could or could not say. In fact, you shouldn't be able to find out who the knight is.

>> 20
Oh, and lastly, since B and C did say "knight", by deduction they cannot be the knight.
No. In principle, it's perfectly possible that no one at all said "knight". For example, if A is the spy, B is the knave, and C is the knight, each could have said the other is a knave. Unless you can exclude that possibility for some other reason.

The key to solving this puzzle is to consider that (methodology spoiler, not the answer) if you had complete information of what each defendant said, you should be able to find the spy like the judge did. This is only true for a few combinations!

>>21
K = knight
N = knave
S = spy

KNS
K: S=S
N: K=NS
S: N=KNS

KSN
K: N=N
S: K=KNS
N: S=KN

What if they give the answers NNN, SSS, NNS, SSN or KNN?

>>22
For that approach to work you will have to write down that scheme for each of the six combinations of the defendants: KNS, KSN, NKS, NSK, SKN and SNK. Then you can check which combinations of statements happen for a single position of the spy.

For example, the statements NNN can be given by defendants NKS or SNK, so the judge would not have been able to tell if the spy was A or C, which means you can exclude the NNN possibility.

>>23
How does that exclude the possibility of NNN or NNK? The spy will want to confuse the judge.

>>24
I'll try to explain it in a different way.

Imagine you're the judge. You know is that A, B and C are one knight, one knave and one spy, but you don't know which one is which. Each defendant comes and makes a statement. You (the judge) hear their statements, so you know what each of them said. What happens next depends on what was said. A couple of examples:

Case 1

Suppose A said "C is a knave", B said "A is a knave," and C said "B is a knave." There are three different ways this could have happened:

A is the knight, B is the spy, C is the knave;
A is the knave, B is the knight, C is the spy;
A is the spy, B is the knave, C is the knight.

So how do you (the judge) tell which one of the possibilities above is the truth? You can't. Your trial fails and the spy gets away.

Case 2

Suppose A says "C is the spy," B says "A is a knight," and C says "B is a knave."

In this case, if A is the knight, C must be the spy, because the knight only speaks the truth, and B must be the knave, since he's the only one left. However, this would lead to a contradiction, as B, the knave, who never tells the truth, said that A is the knight, which is true. Therefore, A must not be the knight.

If A is the knave,  C must be the knight, since A must lie. This leads to another contradiction, as the knight is saying the spy is a knave, which is a lie. So A can't be the knave either.

If A is the spy, then B must be the knave, as he is lying, and C is the knight. Now every statement fits. Since this is the only possibility that would lead to those statements, you (the judge) can conclude that A is the spy.

--

Now, imagine you're the logician. From what you (the logician) have been initially told, you have to consider 18 such cases, including the 2 examples above. However, you know that the judge was able to find the spy, so you can eliminate every case that would result in the trial failing, like case 1.

Once you find out which cases have a unique solution and which don't, you will be one baby step away from finding the spy yourself.