dailysudoku.com

ok, so this all revolves around the 3's... we have this structure on the almost x-wing on 3's in the image

https://i.ibb.co/LDjcvk8H/finnedx-wing.pnghttps://i.ibb.co/GBxz02N/extr001.png
another wa ...

very difficult puzzle. this thing didn't want to give in

since ZeroAssoluto is so gracious to post the grid after basics...

in the image below is an m-wing
(6=7)r3c3 - (7)r9c4 = (7-6)r7c6 = (6)r7c5; r123c5 <> 6
https://i.ibb.co/hJyWpwBT/ds1.png

from the grid posted by ZeroAssoluto,

you can elimiate the 2 in r5c5 by way of the 2's in this simple chain
r4c6 = r4c3 - r8c3 = r8c5... the puzzle then dissolves

for those confused about tom's logic. hopefully this helps.
the chain would be something like this.
(2=4)r3c1 - (4)r89c3 = (4)r8c1 - (4=2)r6c1; eliminates the 2 in r5c3.
this is a W-wing

https ...

https://i.ibb.co/wZTs39JL/xsudo1.png

very appealing visual on the cells containing 159. if all 6 cells contained ONLY 159, you would not have a unique puzzle. you can place the 4 in r4c2 (or eli ...

some m-wing on this holiday

https://i.ibb.co/MnJZkbV/sudoku3.png

(5=8)r6c7 - (8)r6c8 = (8-5)r7c8 = (5)r7c9; r4c9 <> 5

xy-wing completes it
interestingly, the xyz-wing that eliminates the 2 in r4c7 doesn't do anything.

this is the kind of interesting "stuff" that needs to be posted more often. and pinned to the top of some forums for more interesting conversations

+------------+----------+----------+
| 28 1 3 | 28 7 5 | 9 4 6 |
| 49 7 2489 | 3 89 6 | 1 28 5 |
| 6 5 289 | 289 1 4 | 3 7 28 |
+------------+----------+----------+
| 49 3 ...

when sudoku got its attention years ago. this was the first forum I visited.

I had a screen name at the time shortened from my current screen name as "storm_norm"
but since there isn't r ...

this puzzle is hard.
I am finding a fish and an xy-wing to start
then from there you have some pretty difficult chains to make any progress

Yes norm, used something related, believed it was an actual M-Wing, but I came to it via a different path. So many options and good rinsing/scanning skills needed in this one. Thanks again peter.

c ...

almost m-wing Cool

you would have this m-wing
(6=4)r9c9 - (4)r9c5 = (6-4)r8c4 = (4)r7c4
which would eliminate the 4 in r7c7 if the 6 in r8c5 didn't exist.
so following the 6's along (6)r8c5 - ...

this doesn't solve it. If you are looking for a cool way to eliminate some candidates using some Unique rectangle logic then in the image below you can see that the 4's in the UR (46)r56c57 only have ...

shortest path
is xy wing then xy wing?

(2=9)r7c1 - (9=7)r7c9 - (7=2)r4c9; r4c1 <> 1

then

(7=3)r4c7 - (3=9)r8c7 - (9=7)r7c9; r4c9 <> 7

Thanks for checking that storm_norm! Hey, I see that you just joined! Welcome!

thank you.

actually my second sign up. was gone for so long that my other account was deactivated.

from dongrave's grid

(8=9)r7c5 - (9)r7c1 = (9-5)r8c1 = (5)r9c2 - (5=8)r9c7; r7c9 <> 8

Here's the grid after basics:

+-------------+------------------+-----------------+
| 9 1258 28 | 7 3456 1345 | 238 268 123568 |
| 3 125 6 | 8 9 15 | 7 4 125 |
| 4 ...

+----------------+---------------+-----------+
| 58 7 6 | 58 2 4 | 9 3 1 |
| 4 9 2 | 7 3 1 | 5 6 8 |
| 358 38 1 | 568 9 68 | 7 2 4 |
+------- ...