Rules of Slitherlink:

  • Connect adjacent dots with vertical or horizontal lines to make a single loop.
  • The numbers indicate how many lines surround it, while empty cells may be surrounded by any number of lines.
  • The loop never crosses itself and never branches off.

enter image description here

  • 1
    $\begingroup$ Link to Penpa version (let me know if there's a mistake, I transcribed this manually) $\endgroup$
    – HTM
    Commented Apr 1, 2021 at 4:52
  • 3
    $\begingroup$ Haha! I had a feeling the seasonal tag was going to prove appropriate here! :) $\endgroup$
    – Stiv
    Commented Apr 1, 2021 at 6:03
  • 1
    $\begingroup$ @Stiv yeap, adding the tag :) $\endgroup$
    – athin
    Commented Apr 1, 2021 at 8:34
  • 1
    $\begingroup$ An alternative (and perhaps superior?) version of the joke involves a rot13(yratgu fvk ybbc fheebhaqvat gjb guerr pyhrf) :) $\endgroup$
    – happystar
    Commented Apr 1, 2021 at 9:07
  • $\begingroup$ @happystar yes!! I once found it published by someone and I was dumbfounded :)) $\endgroup$
    – athin
    Commented Apr 1, 2021 at 9:19

1 Answer 1


The solution is (drumroll please...)

around_the_w0rld_sol Yep, that's it. All those clues for just a measly square. (I guess that's why this puzzle's tagged !)


We start by

marking the edges where the loop cannot pass through due to the 0 clues: around_the_w0rld_1


we progressively mark off edges coming off of dots where the other three edges (two for a border dot, one for a corner dot) coming off of them are marked as unusable. We continue to do this until we reach a state like this - note the square at R10C16: around_the_w0rld_2

And here's the coup de grâce:

It appears that we're able to make a connected loop spanning the entirety of the grid, but actually we can't (!) due to the edge marked with the star below not being usable: around_the_w0rld_3 Thus, we are forced to use the square mentioned earlier for our loop, giving us our final solution.

  • $\begingroup$ Nicely done and well explained! XD $\endgroup$
    – athin
    Commented Apr 1, 2021 at 8:35
  • 2
    $\begingroup$ @athin Thanks, this is a really nice construction! $\endgroup$
    – HTM
    Commented Apr 1, 2021 at 8:37

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