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swando



Joined: 09 Mar 2009
Posts: 20
Location: Surrey, BC. Canada
PostPosted: Sun Feb 09, 2025 5:39 pm    Post subject: stumped Reply with quote
can someone explain why 9 is required in top left had corner box?


Code:

+-------------+---------------+--------------+
| 89  3678 37 | 5    2   38   | 69  4   1    |
| 458 3568 1  | 9    7   348  | 2   368 38   |
| 489 38   2  | 134  6   1348 | 5   389 7    |
+-------------+---------------+--------------+
| 1   35   9  | 2346 45  7    | 8   236 234  |
| 58  3578 37 | 2346 459 3469 | 469 1   2349 |
| 2   4    6  | 13   8   139  | 79  379 5    |
+-------------+---------------+--------------+
| 6   2    8  | 47   3   5    | 1   79  49   |
| 7   9    4  | 8    1   2    | 3   5   6    |
| 3   1    5  | 467  49  469  | 479 28  28   |
+-------------+---------------+--------------+

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glesco



Joined: 12 May 2022
Posts: 39
Location: North Vancouver, BC, Canada
PostPosted: Sun Feb 09, 2025 10:33 pm    Post subject: Reply with quote
OK, I'll give a try especially since your a fellow Metro Vancouverite! I do these puzzles with pen and paper so hopefully you are able to follow my narrative. I used three steps from your board.

1st. Cell r9c7 can not be a 9 because all the possibles in r7 are in box 9.

2nd. All the possible 9s in box 3 are all in c78 which creates a W-wing with the two 79 pairs, eliminating 7s from r6c8 & r9c7. r9c7 is now a 4 which allows completely solving r9 with a 9 in c6. Cell r5c5 is now a 45 pair.

3rd. There is now an XY-chain on 8s with the anchors at r3c2 & r5c1. The travel path is through r4c2, r4c5, r5c5. That eliminates 8s in r123c1 & r5c2.

Let me know if you found this helpful. Regards
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glesco



Joined: 12 May 2022
Posts: 39
Location: North Vancouver, BC, Canada
PostPosted: Sun Feb 09, 2025 11:14 pm    Post subject: Reply with quote
Ooops! In "Step 2," the 9 in r9 is in c5. Sorry
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glesco



Joined: 12 May 2022
Posts: 39
Location: North Vancouver, BC, Canada
PostPosted: Sun Feb 09, 2025 11:22 pm    Post subject: Reply with quote
A typo, logic still works!
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swando



Joined: 09 Mar 2009
Posts: 20
Location: Surrey, BC. Canada
PostPosted: Mon Feb 10, 2025 6:43 pm    Post subject: Reply with quote
Thxs..the 79 Y Wing got me..I haven't done Sudoku for a few years and forget
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