Is This Puzzle Too Hard?

[Mouser]

My favourite solution to the conundrum of "which monster lies?" is one I, as DM, was exposed to in D&D...

The Bard of the party steps up to one of the monsters.

"What's 2+2?"

"...aw, ffff....ive."

It really only becomes a "puzzle" when you are allowed to ask exactly one question.

In that case you have to phrase it so both of them will give you a truthful response.

 

[Vinedrius]

When you speak to LM, you get these responses:
1. My sister (edit: this is referring to RM) would say I always tell the truth.

When you speak to RM, you get these responses:

1. My sister (edit: this is referring to LM) would say I always lie.

If we assume that LM is telling the truth, then RM must be lying and if that is true, then LM must be lying.

If we assume that LM is lying, then RM must be telling the truth and if that is true, then LM must be telling the truth.

If we assume that RM is telling the truth, then LM must be telling the truth and if that is true, then RM must be lying.

If we assume that RM is lying, then LM must be lying and if that is true, then RM must be telling the truth.

In other words, every option ends up contradictory in itself so you can't trust either of them imo and I don't even think we need to look at other responses at all since you have said that we could solve it by only using the responses of one of them. But this is also ignoring the fact that you have given the information in the beginning that they both say 4 people died and then LM says that R survived. In that case, the puzzle already falls out of context because there is not much to solve anymore since LM is obviously lying.

Day 1You left S behind in the starting village to defend it on his own. It looked bleak, but it was a choice of two bad options.

K and N were removed from your party after a cave collapsed, separating you from them. They were trapped behind.

Day 2

R was removed from your party after you fought her.

You've eventually arrived at this logic puzzle.

When you speak to RM, you get these responses:1. My sister (edit: this is referring to LM) would say I always lie. (doesn't matter anymore)

2. N died last.

3. S died today.

4. K died instantly when a boulder crushed him.

5. R died before S.

N = 4th

K > R & S

R > S

Thus; K > R > S > N

 

[Kyutaru]

If we assume that LM is telling the truth, then RM must be lying and if that is true, then LM must be lying.

If we assume that LM is lying, then RM must be telling the truth and if that is true, then LM must be telling the truth.

If we assume that RM is telling the truth, then LM must be telling the truth and if that is true, then RM must be lying.

If we assume that RM is lying, then LM must be lying and if that is true, then RM must be telling the truth.

Incorrect logic path.  If we assume that RM is telling the truth, she is claiming that LM would say that RM is a liar.  For LM to claim that RM is a liar, LM would have to tell the truth about RM.  However, RM is already telling the truth that LM would claim she's a liar.  If RM were a liar, she couldn't be telling the truth.

It is correct to assume that RM is telling the truth, but also that LM is lying.  LM would lie about RM and say that she "always lies", which RM reports as the truth (note she's only saying what her sister WOULD say).  For LM to accuse RM of being a liar when RM obviously tells the truth, LM would have to be a liar.  This is supported by LM's statement that RM would claim she "always tells the truth".  RM is a truth teller and would NEVER claim that a liar like LM tells the truth, so LM is obviously lying once again.

Same result, but it's definitely powerful to conclude accurately that LM always lies and RM always tells the truth.

 

[Vinedrius]

Incorrect logic path.  If we assume that RM is telling the truth, she is claiming that LM would say that RM is a liar.  For LM to claim that RM is a liar, LM would have to tell the truth about RM.  However, RM is already telling the truth that LM would claim she's a liar.  If RM were a liar, she couldn't be telling the truth.

Assumption: RM tells the truth.

The only information about what RM would claim is that LM always tell the truth. => LM tells the truth.

The only information about what LM would claim is that RM always lie => RM lies.

I am just following the string and honestly can't see how this path is wrong :s To lie, you have to know the truth first so when we start with an assumption, we have to follow through where it leads us, right? The final destination contradicts the starting point and that is all I am seeing or maybe I am mentally blind orz.

 

[Kyutaru]

Assumption: RM tells the truth.

The only information about what RM would claim is that LM always tell the truth. => LM tells the truth.

The only information about what LM would claim is that RM always lie => RM lies.

You're misinterpreting the information.  RM isn't claiming that LM always tells the truth.  That's what LM claimed she would say.  LM is a liar who knows her truthful sister RM would never say such a thing.  The only thing RM actually said was that LM would claim RM always lies.  If LM is a liar, of course she would claim her truthful sister always lies.  That's what liars do.

LM = RM claims I tell the truth. <-- This a lie, RM would actually claim LM always lies.

RM = LM claims I always lie.  <-- This is the truth, LM would lie about RM telling the truth.

Or to put it another way...

Assumption: RM is telling the truth.

1) RM claims that LM would say she always lies.

2) Since we're assuming RM tells the truth, that can't be possible.

3) LM would have to lie about RM for it to be true.

4) Going to LM's statements, LM claims RM says she always tells the truth.

5) We are still assuming RM tells the truth.

6) If LM always told the truth, then RM would be lying about her.

7) If RM were the liar, and LM told the truth, then LM would need to have said that RM always lies.

8) Except RM did state that LM would claim she always lies.

9) That would be a truthful statement and conflict with the statement that RM always lies.

10) Therefore, the statement is false.  LM is the liar and RM tells the truth.