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I am not new to solving a sudoku board, but I do not have a lot of experience with harder boards and more advanced strategies (I am able to solve a "hard" board in under 10 minutes, on average). I am currently trying to solve an expert rated board without guessing at all, and have come to a point where I cannot figure out how to continue.

board

I have been researching some more advanced strategies, and have recognized a Y-wing: [48] at R6C4, [14] at R5C6, and [18] at R6C7. However, I am unsure how to fully execute this method.

I have been referencing this site (found through this post), but I get stuck when trying to figure out which numbers I can eliminate.
As I am currently writing this, I am continuously referencing the linked post as well as the website, and have come to the guess that 1 will be the candidate that I could eliminate (my reasoning being that R5C6 and R6C7 share the number, but cannot "see" each other). At this point, I am just unsure as to where it can be eliminated. My instinct says it can be eliminated from R5C4, but I cannot provide a logical explanation for that.

Is my reasoning correct for assuming that 1 is the candidate to be eliminated? And
What would be the reasoning for determining which specific cells the candidate can be eliminated from?

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1 Answer 1

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I don't think your Y-wing logic quite works since the two squares with 1 don't both see R5C4. Obviously one of them needs to be 1 or R6C4 has no options, but only one of them would prevent R5C4 from being 1 so you can't eliminate it based on that alone.

However, there's a simpler way to continue here. You have a 148 triple in the central box, which forces the two remaining squares to be a 26 pair. This forms a 26 pair in the central column which in turn gives you a few digits to go with.

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  • $\begingroup$ Ohh okay, I think I understand the application of the Y-Wing now. In terms of the 148 triple, when could something like that be applied? Would they all need to be in the same box like they are there? I have not solved using a triple like that before, so I am trying to get a general idea of when they can be used $\endgroup$ Dec 19, 2022 at 3:10
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    $\begingroup$ Either in the same box, or all on the same row or the same column. If three cells only have three options between them, all three digits must be in some of those 3 cells. Which means you can rule those digits out from other cells in that box (or column, or row). Of course there's nothing special about the number 3 there, you can have a four-digit four-cell quadruple which works exactly the same. $\endgroup$
    – Jafe
    Dec 19, 2022 at 3:13
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    $\begingroup$ (Maybe a simpler of looking at the same thing is to see that 2 and 6 only have two cells where they can go in the central box, so those two cells must contain both 2 and 6.) $\endgroup$
    – Jafe
    Dec 19, 2022 at 3:15

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