Puzzle Description:

The aurora borealis may be seen from many of the northern US states tonight. If you live in the north try going outside tonight. Give yourself 20 minutes to get dark adapted. No outdoor lighting or cell phones. If you spot them, give a comment on this puzzle with city, state, time and your impressions. Fresno CA is probably too far south so let me live vicariously through you.

#1: besmirched tea (Besmirched Tea) on Sep 29, 2020 [HINT] [SPOILER]

I live in Portland, and I've never seen it from here.
I'll give it a go, though.

Is there a name for stair-step logic?
That's what I used on this one.

I feel like I guessed my way through this. It's at *least* moderate lookahead.

Nice.

I have to agree. The Northern Lights are awesome and beautiful. We used to travel the length of Britsh Columbia twice a year. From the North Western corner to the South Eastern corner. We found the best place to view the lights was around Fort Nelson. I have seen stuff that very few people have seen. I have seen red, yellow, green, white. I have seen them in sheets and in ropes that twine together across the entire sky. I have seen them shooting up like you see in iconic pictures. We used to sleep in the vehicle or throw a sleeping bag down on the ground. My husband would sleep (he did the driving) and I would lay awake all night watching. I never believed that sometimes you can hear a whistle but once in the Yukon I heard it. We lived in a very remote area. I admit it still could have been something else but...To anyone who hasn't seen them then it is worth a trip just to do so. You will never regret it!

cooool!! Also used stair-step logic.

I have seen them in varies locations in western Canada, but the best by far that I have seen were in Yellowknife, where you can hear them hum.

I didn't know there was an auditory component. The northern lights remain on my bucket list.

I'll put my vote in for deep lookahead. I was able to place stuff on the edges but repeatedly had to use tricky edge logic e.g. where exactly to place the green 4/3 in C20.

Very entertaining though. I had to do a lot of deep edge logic after this to get things going. I worked on column 7 along with the 4 in column 4 in the meantime too. I suspect a bit of educated guessing from the title (ribbons meaning we don't have 2x2 green clumps) might help things go quicker here

Initial line & color logic gets to 37% with the black finished but no greens placed.

C1: EL marks R1-3 white.

C20: EL marks R4 and R10 green. (Once R4 is placed to start the 4, you can use additional EL to find R10 for the 3 if you keep track of how many 2s are accounted for in C19.) LL.

C20: Whether the 3 goes into R11 or R9, R9C19 is green. Minimal LL.
C20: EL now puts a green in R3. LL.

C18: If the 2 is in R4-5, it means the 3 is in R7-9 and it makes C17 invalid. Therefore the 2 must be in R1-2. LL.
C18: We can now use EL to place green in R7-8. LL.

C20: If the 3 goes into R8, it makes C17 invalid, so R11C20 is green instead. LL.

R15: Wherever the green 1 goes, it extends into R14. R14 C6-7 and C10-17 are white.

C3: If the 2 is in R14-15, there's no valid way to place C1-2 (wherever the 5 is placed, at least one of the 4s will need to cross a 2 that the 5 doesn't reach). R14-15C3 are white.

C1: Wherever the 5 is placed, R12C2 is green.

Deep lookahead C2: If the bottom 4 goes up to R9, at least one of R10 or R12 would have to go into C1. Since that column would be blocked at R9, either one of those would make R11-14 C1 green, which means the first 2 in R10 would have to go into C1 as well. This would complete R14 without placing any green into C15, which means that green 1 has nowhere to go.
TL;DR: R13C2 must be green.

C1: If the 5 does *not* extend to R4, then R4C3 will be green. If the 5 *does* extend to R4, then R12C3 will be green. Therefore, R1-2 and R6-10 in C3 are white. (This step also shows the 5 can only either go in R4-8 or in R8-12, since placing a green in R4C3 would also place one in R12C1.)

Deep lookahead C4: If R4 is green, the 5 in C1 would be in R4-8 and the top 4 in C3 would be in R1-4. From there, the only position for the 4 in C4 that doesn't make C5 invalid is R4-7, so we can safely mark R1-3 C4 white.

Deep lookahead C1-4: If the 5 in C1 is in R4-8, it puts the top 4 in C2 into R1-4, and the bottom 4 in C2 into R12-15 (since we can't complete R14 without also completing R15). This puts the 2 in C3 in R11-12 and the 2 in C4 into R10-11, which means R5-7 C4 must also be green. If the 5 in C1 is in R8-12 instead, the bottom 4 in C2 goes into R10-13, and green is placed in R4C3. R4C4 will be white. Using EL on this proposed placement, we can determine the 4 in C4 can't go below R10 in this scenario, which would put greens in R7-8. In both of these situations, R7C4 must be green. Minimal LL.

Deep lookahead C5: If the 3 is placed in R13-15, it triggers the second of the scenarios in the previous step (5 in R8-12 C1). In addition squares I listed there, we know that either R5 C2 or R5 C3 will be green, which will account for the first 1 in R5. We also would be unable to place the 2 in C4 below R10-11, which nudges the 4 in C4 to include R6. From there, either R5 or R8 will trigger the 2 in C5, but all remaining positions for the 2 in C4 would also trigger the 2, thus making C5 invalid.
TL;DR: R14-15 C5 must be white.

[As an aside, I'm starting to feel a little like I'm channeling Vizzini with this dizzying logic right about now.]

Deep lookahead C4: Placing a green in R12 would trigger C1 placement B (5 in R8-12), but now that we've marked R14-15 white in C5, C1B requires the 2 in C4 be placed in R14-15. Since R12 is too far away to be part of the 4, this move is invalid, and R12C4 must be white. We can mark R13C4 white also, since that would complete R14 without placing the green 1 in R15.

Deep lookahead C5: C1 placement A (5 in R4-8) puts the 2 in C4 into R10-11, and the 3 in C5 into R8-10. C1B makes the 4 in C4 go down to at least R8, which triggers one of the clues in C5. Either way, R8-9 C5 are green. LL.

Deep lookahead C5: If the greens in R8-9 are the 2, this puts the 3 in R11-13 and triggers C1B. This would make C10-16 white for R9, R11, and R13. The remaining 1 in C14 could go into C20, but there is nowhere for the remaining 2 in R10 to fit. Therefore, R8-9 C5 must be part of the 3 instead, and R10C5 is green. LL.

C6: If R13 is green, this makes C7 invalid, so this square is white.

Deep lookahead C6: If R10 is green, it marks R12C6 white, which marks R11-13 C7 white, which then marks R11C6 white and then R9C6 green. This triggers C1B and places the green 4 in C4 into R5-8, and this places the top 4 in C2 in R4-7. Next this puts the 2 in C5 into R4-5 and the 1 in C6 into R4. This would fully solve C1-6, but there's nowhere left to put the 3 in C7 that doesn't make C6 invalid. Therefore, R10C6 is white. Minimal LL.

Deep lookahead C6: In C1A, the green in R9C5 is the 1 in R9. In C1B, the green 4 in C4 will now need to be in R7-10. In either scenario, R9C6 is white.

OK, even with how deep in the woods I am right now, I'm having trouble finding a definitive next step. Going to give this one a break for a while.

Goto next topic

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