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Jun. 14th, 2017 @ 02:01 pm Five bags, four possible answers, three logic puzzles, two liches and one treasure
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OK, so before the bizarre misunderstandings in my previous post, I had been going to repost question which I thought was an interesting logic puzzle in its own right.

You have five bags of holding. One contains a fabulous treasure. Two contain liches who can't escape until you open the bag. Two contain nothing.

You have a spell which tells you something about the result of a course of action you propose. (This description is slightly altered from the functionality of the original spell to make the puzzle work, feel free to ask for clarification as needed.)

"Weal" for good result (eg. treasure, no liches)
"Woe" for bad result (eg. 1+ lich, no treasure)
"Weal and Woe" for a good and bad result (eg. treasure and also lich)
"Nothing" for a result of no particular good or bad (eg. open no bags or only open empty bags)


What's the minimum number of castings of the spell needed? (I think 3 is easy and 1 is impossible, so basically, can you do 2?)


The course of action has to be 30 minutes or less.

We don't have specifics on how you define the course of action, ask if it needs to be more explicit.

Assume you can include other results in the plan if they help, eg. "if this bad contains nothing, I stab myself in the leg", without necessarily needing to follow through. (This is slightly more generous than the original spell.)

Assume you don't include the castings of further divination spells within the scope of the course of action considered by casting the first spell.

Follow-ups (may be unnecessary depending on the best solution to the original)

If you only have one casting, what's the greatest chance you can give yourself of finding the treasure whilst finding no liches.

The original restrictions of the spell say that if you cast it four times in a day (ignored for the basic puzzle), the second, third and fourth times have a 25%, 50% and 75% chance of giving a random answer. What's the highest chance you can give yourself of finding the treasure and no liches in up to four castings with those failure chances.

Previously we assumed you couldn't create a paradox. If you *can*, and causing a paradox causes the spell to fail to give an answer in a way distinct from "nothing", can you reduce the number of castings?

If you *can* ask about a course of action including further divination spells, does that help?

Does the answer generalise to a larger number of bags (assuming 1 treasure, N liches and N nothing)

ETA: Fix formatting.

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Date:June 14th, 2017 04:33 pm (UTC)
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I think it's doable in two castings. Don't scroll down if you're reading this and want to have a go for yourself.


My attempt

Define the bags as A, B, C, D and E
Cast spell with plan: "Open bags A and B":
"Good": Action: Open bags A and B
"Bad": Cast new spell as defined in (1)
"Mixed": Cast new spell as defined in (2)
"Nothing": Cast new spell as defined in (1)

(1) Plan: "Open bag C, stop if it contains treasure. If not open bag D"
"Good": Action: Open bag C. If bag is empty open bag D.
"Bad": Action: Open bag E
"Mixed": Action: Open bag D
"Nothing": Action: Open bag E

(2) Plan: "Open bag A"
"Good": Action: Open bag A.
"Bad": Action: Open bag B.
"Mixed": Reboot universe
"Nothing": Reboot universe

Should require one casting 40% of the time, two castings 60% of the time.

Edited at 2017-06-14 04:40 pm (UTC)