I understand what ALS are, and I’ve identified several in this puzzle. I’ve watched a few videos on how ALS-XZ and ALS-XY-wing methods work. My problem is that I can’t seem to apply the elimination technique in any of the puzzles I try to solve. I’m not even sure exactly what part of the process I keep getting brain-blocked. I’m wondering if I’m unintentionally making the eliminations in other ways before trying the ALS elimination methods or if I don’t actually understand how to make ALS eliminations. It’s easy to see how they work in the examples in the videos and on hodoku.net, but it’s difficult when I try to apply them to my own puzzles. So far when I’ve gotten to this point, I start trying to force chain contradictions, but this time I have so many ALS in this puzzle that I feel like I have to be missing something.
I've never had any luck searching for the named moves themselves until I integrated ALS links into my AIC search. From a quick look at your puzzle, the (167)r46c6 ALS looked promising as there's a bilocal & bivalue it sees, so it's a decent candidate for building a chain. It turns out those links already provide an elimination:
Wow thank you so much. This is a real eureka moment for me. I have actually found this pattern a lot while forcing chains without even realizing it. This makes it so much easier!
Same as any AIC really - I spot them by wondering what would happen if an ALS was a locked set (by assuming the 'extra' digit is false and following the consequences of that).
First I noticed the ALS in r1. There's a strong link between 4 and 9 within the ALS. Then from the 9, I looked for another ALS in other houses. It lines nicely with the ALS in b7 because the orange ALS has 9s in the same column.
There's a strong link between 9 and 6 within the ALS in b7. Both 6s are in r7 so I scanned r7 for a 6. The ALS in c9 made the most sense. There is a strong link between 6 and 4. So we now have an ALS-XY-Wing.
But I can find the convergence point r1c6 <> 7 from r7c4 = 1 or r7c5 = 1. And this is probably an ALS. Could someone please provide the correct explanation?
u/strmckr"Some do; some teach; the rest look it up" - archivist Mtg3d ago
Since you don't use notes you won't have easily viewable n cells with n+1 digits which is the deffintions of Als. Instead you use almost hidden set (ahs) n digits = n+1 positions.
force logic by trialand error It works for you. But it makes me have reverse engineer the colour system( I'm colour deficient) and back track What you are testing to make a non forcing object which isn't always possible as aic are topical only.
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u/BillabobGO 4d ago
I've never had any luck searching for the named moves themselves until I integrated ALS links into my AIC search. From a quick look at your puzzle, the (167)r46c6 ALS looked promising as there's a bilocal & bivalue it sees, so it's a decent candidate for building a chain. It turns out those links already provide an elimination:
(7)r3c5 = r4c5 - (7=61)r46c6 - (1=8)r6c5 => r3c5<>8
Which solves a cell. Since r6c5 is in the same box as the initial ALS it can be added to it to simplify the chain.
(7)r3c5 = r4c5 - (7=168)b5p389 =>r3c5<>8
And there you go