### Slitherlink (Portal) by Bobby Liu

PDF

or solve online (using our beta test of Penpa-Edit tools in edgex mode where left click+drag draws lines and right click marks X’s)

Theme: Connected Logic

Author/Opus: This is the 1st puzzle from guest contributor Bobby Liu.

Rules: Standard Slitherlink rules. Also, there are four regions (in gray) in the two grids that are portals. All edges that touch any gray squares must match across grids (without rotation or reflection). For identical shapes, it is not known which positions are matched (for example, the ring in the upper left of the first puzzle could be in either the upper left or lower right of the second puzzle).

Answer String: Enter the length in cells of each of the internal loop segments following the arrows for the marked rows, starting at the top. Separate each row’s entry with a comma.

Time Standards (highlight to view): Grandmaster = 18:00, Master = 30:00, Expert = 1:00:00

Solution: PDF; a solution video is available here.

• Jack Bross says:

This was a triumph!
I’m making a note here:
“Huge Success”.
It’s hard to overstate
my satisfaction.
😀

There were some interesting big logical ideas that you needed to figure out to get going, which definitely made this more interesting than the usual slitherlink.

• John B says:

Basic agreement with Jack. A real uphill climb and some nice logic; I liked each bottom left corner.

IMHO, it would have been easier for me if 12 numbers had been removed (this can be done with 2-way if not 4-way symmetry)! Then I would’ve had to work on the divide-and-conquer strategy much earlier and gotten to the interesting part faster. As it was there was enough apparently useful data to keep me in the ruts instead of the high ground, and there was enough tantalizing as to how to use the portals that one didn’t feel comfortable drawing any useful conclusion. But once you get the strategy, wow.

Mental note: don’t try to copy from one portal to the same-size portal in the same grid, which I tried twice.

• Really tough, and really fun.

I proceeded through the same sequence of “aha!” moments that Thomas Snyder describes in his video walkthrough for Patreons – albeit about ten times as slowly!

I also note that once you’ve determined that the ovt evat cbegnyf fjnc cbfvgvbaf, then some simple pbaarpgrqarff shows they must have bccbfvgr vafvqrf naq bhgfvqrf. As a result I found the technique of pbybevat vagrevbe naq rkgrevbe pryyf that I sometimes use when Slitherlinking was especially useful for this puzzle.

• Aaron Chan says:

This was both tough and very neat.

• swaroop says:

such awesome and brilliant puzzle.
Lot of different logic were used to solve this.
Took lot of time but as i got involved got different thoughts probably next one i could do it fast if any 🙂

• David Olmsted says:

To clarify the rules: Only an edge in the gray area, or along the edge of a gray area has to match. An edge which touches a gray area only at a corner does not have to match.

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