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HappyDog

Joined: 11/11/2015 18:26:16
Messages: 78
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Number: Puzzle #1546
Genre: Mine Shaft
Author: Maarten
Appeared at: November 28, 2009

It would be useful if the instructions for Mine Shaft were updated to state whether or not loops are allowed.

I am in the middle of this puzzle, and there are possible routes forward which would create a loop, but which otherwise satisfy all the constraints of the puzzle.

I will have to pursue these options, as I obviously can't assume they are disallowed in case that is incorrect, but it's a bit frustrating not knowing whether I'm wasting my time (and potentially on the way to finding alternative solutions that are not actually allowed).
edderiofer

Joined: 16/06/2012 16:15:22
Messages: 234
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I'm fairly certain loops are allowed, though I'll have to ask Thierry or someone to verify this for me.

Once we have an answer, I'll put that in the rules.
JHe

Joined: 01/12/2011 11:39:39
Messages: 100
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"The shaft cannot touch itself, not even diagonally."

I have solved them all, and I'm quite sure that I haven't breached that rule in any. That would mean the solutions exist without loops.

But it's good that you ask the official stance, and change the line if needed.
HappyDog

Joined: 11/11/2015 18:26:16
Messages: 78
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Not necessarily - it is possible to have a loop without the shafts touching diagonally.

A trivial example:

Code:
```     o o o o o
X o o       o o X
o o o o o
```

With appropriate numbering, this would not break the uniqueness criteria, nor the touching tunnels rule.
JHe

Joined: 01/12/2011 11:39:39
Messages: 100
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That is what I have avoided - I see two shafts there, and they meet in full frontal at two places.

So I'm quite sure the solutions don't have any of that. But let's wait for the official declaration.
edderiofer

Joined: 16/06/2012 16:15:22
Messages: 234
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The official decision is that Mine Shaft puzzles do not contain any loops. I've added this to the English rules and am currently waiting for one of the moderators who know Dutch to add them to the Dutch rules.
HappyDog

Joined: 11/11/2015 18:26:16
Messages: 78
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Thanks for the clarification. This particular puzzle was incredibly hard to solve if you assume loops were allowed.

In amongst the many loop-based blind alleys, there was one solution which has some large loops going across the board, where the only issue is that the left column has 15 bits of shaft instead of 14... and you only find that out once the whole grid is filled. Knowing that loops are disallowed would probably have shaved about 3 hours off my solve time, or more!

Good to have a resolution to this, for future solvers.
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