### From the Foxger’s Den #34: Double Back

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

This is a bonus “Twisted Tuesday” puzzle variation.

Theme: None?

Rules: Standard Double Back rules (originally from MellowMelon). In short: draw a single loop that enters and exits every cell exactly once, and enters and exits every region exactly twice.

Answer String: Enter the length in cells of the horizontal loop segments from left to right in the marked rows, starting at the top. If the loop only has vertical segments in the marked row, enter 0. Separate each row’s entry with a comma.

Time Standards (highlight to view): Grandmaster = 2:15, Master = 3:30, Expert = 7:00

Solution: PDF

• Vraal says:

Grant, I really enjoyed this puzzle pair; I actually solved both atop each other. =)

• Aaron Chan says:

How does someone make a puzzle like this?

• Para says:

It’s really not much different than designing other puzzles. You try to find openings that work for both puzzle types and progressively keep track of the progress in both and look for options that work in both puzzles. Sometimes this can be pretty easy as it’s already pretty much settled in one type. For example when you look at these puzzles, you’ll see that a few times in the double back you are forced to go in and and a region because of the rest of the loop. This means you have a lot of freedom shaping this region for the LITS puzzle as long as all the remaining cells can be connected with a single line.
You’ll see that generally this gimmick leads to puzzles having a similar solving path as clues are used in both puzzles in generally the same order.

• edderiofer says:

3:44. The 4-cell and 6-cell region at the very top left of the puzzle is where I lost quite a bit of time. Also the fact that I haven’t played this genre for such a long time…

• chaotic_iak says:

The same as usual puzzles? Only that you must be careful to keep each puzzle to have a solution, and at the end, to make sure each puzzle has only one solution. More difficulty if you want to make a theme. From my experience, making a double puzzle like this is usually as tough as making a complex puzzle (has many nontrivial deductions and/or has complicated rules) to work as expected. Of course opinions can differ. Perhaps Para (Bram de Laat) can speak about this matter better?

• chaotic_iak says:

(Crap. My previous comment is replying to Aaron Chan’s comment, and for whatever reason my phone acts up to cancel the “replying to” field but not the comment, leaving a non-indented comment as above.)

• skynet says:

24 mins.Would love to see more of these double back puzzles. Had good fun solving it.

• Francis says:

Never seen this type before — took me a while to get the hang of it, and then I was surprised at how much speedier the solving went once a few areas got nailed down.

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