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I have been working on a Knapp Daneben Tapa, where each clue is wrong by exactly one unit. I have tried it a few times and keep running into the same problem. I think I am solving it deductively/not making any guesses, but I wind up with a clue not being satisfied. I am including the puzzle below. I am not sure how crediting people for puzzle creation really works (I'm new to the site), but including a link to where I got it from as well. I am looking for either a solution/some steps for comparison with what I did, or confirmation that I am indeed running into a real contradiction. I got the puzzle from the following link: http://oapc.wpc2009.org/archive.php?id=52

Here is a screenshot of the puzzle itself:enter image description here

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  • $\begingroup$ Welcome to Puzzling! You've cited the original source pretty much perfectly, thank you :) $\endgroup$
    – Rubio ♦
    Aug 27, 2019 at 3:42

2 Answers 2

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Agreed, there is something wrong.

I arrived straightforwardly at the following situation:
enter image description here
and there is no way to complete the top.
For the record, here are some intermediate situations:
enter image description here
enter image description here
enter image description here
Note: you complete the 7 by seeing an immediate contradiction if the other choice is made. The next step after this last picture is to see that exactly one of the two empty squares [lying above the inverted C at the bottom] has to be filled (at least one for connectedness and not two because of the 2x2 square rule), and there is an immediate contradiction if you fill in the other one.

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  • $\begingroup$ Thanks! Aside from the top left corner, where I run into the problem a little differently than you do, I agree with your solution! $\endgroup$
    – Jobo
    Aug 26, 2019 at 23:33
  • $\begingroup$ @Jobo If you agree with my very first step then the top-left can only be as shown, because the 7 can only be filled in one way as explained, and then the 1 1 3 square can only be surrounded by even length strings, and finally you apply the 2x2 square rule to rule out 5 around the top-left 1 4 square. $\endgroup$
    – Arnaud Mortier
    Aug 26, 2019 at 23:39
  • $\begingroup$ Oh my bad! You are right! I had erased some stuff and tried playing with it to see if I could hack my way to the answer. I actually originally ran into the problem in the same spot you did. $\endgroup$
    – Jobo
    Aug 27, 2019 at 1:07
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This puzzle is indeed broken, and has no solutions. (I ran into the same contradiction as Arnaud.)

The organizer, Serkan Yürekli, made a post on the Logic Masters Deutschland forum around that time, confirming this. The 1,1,3 clue at the top was the problem, and because of this they ignored the top arrow when checking solution keys.

enter image description here

(In addition, the Tapa ? from that contest has multiple solutions - so if you're going through the archives, you may want to keep that in mind.)

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