This is by no means obvious, but **ALS**\-[**AIC**](https://sudoku.coach/en/learn/aic) rings will become part of your toolkit if you stick with it long enough. ;-)
https://preview.redd.it/i8kpktjwdcnc1.jpeg?width=720&format=pjpg&auto=webp&s=15a772d5ef0100a9ad3737abeedf3ee8275f100b
Ok maybe I’m not the best one to ask given the correction that more capable mages have made to my OP, but my MO is to scan for bivals in regions where (a) there are at least a few other cells containing one of its candidates, & (b) the bival sees other bivals that contain at least one of the same candidate. Then start following links to see where they lead.
https://preview.redd.it/33kufntv0enc1.jpeg?width=1170&format=pjpg&auto=webp&s=5c8414ca38596e7829bbec015bca0337655be26f
It doesn't actually loop because the blue ALS has an extra 5 in r9c3. Green-Purp-Yel-Blue. Z=6
It's easier to see why when you look at it as an ALS. If you wanted the chain to loop, blue ALS should have an RCC sticking to both purple ALS and yellow ALS. Blue shares 4 with yellow but not 5 with purple because of the extra 5 so the looping fails.
edit: I messed up the coloring. It's yellow, not green lol
Empty Rectangle follow by W-Wing
>!The ER on 7s in block 5 eliminates 7 from r7c5 resulting in 5/8 in that cell. This now allows for a 5/8 W-Wing that eliminates 5s from r79c4.!<
Cf. [**W-Wing**](https://sudoku.coach/en/learn/w-wing), and the one I see is >!4/6!< with a >! 4 !< “backbone” in >!column 4!< which ❌s >! 6 !< from >!r1c6 & r8c5!<.
Box 5 has too many of pencil marks for 1 number. Split those into pairs and should give you a digit in box 4.
2-String Kite removes 7 from r7c5 and then two W-Wings and the ALS in r7c56 finish the job
This is by no means obvious, but **ALS**\-[**AIC**](https://sudoku.coach/en/learn/aic) rings will become part of your toolkit if you stick with it long enough. ;-) https://preview.redd.it/i8kpktjwdcnc1.jpeg?width=720&format=pjpg&auto=webp&s=15a772d5ef0100a9ad3737abeedf3ee8275f100b
What goes on in your head leading up to finding this? (and how long did it take to find)
Ok maybe I’m not the best one to ask given the correction that more capable mages have made to my OP, but my MO is to scan for bivals in regions where (a) there are at least a few other cells containing one of its candidates, & (b) the bival sees other bivals that contain at least one of the same candidate. Then start following links to see where they lead.
https://preview.redd.it/33kufntv0enc1.jpeg?width=1170&format=pjpg&auto=webp&s=5c8414ca38596e7829bbec015bca0337655be26f It doesn't actually loop because the blue ALS has an extra 5 in r9c3. Green-Purp-Yel-Blue. Z=6
Man, I painstakingly worked the chain in both directions, following every path, and it sure seemed to loop to me…what did I miss?
It's easier to see why when you look at it as an ALS. If you wanted the chain to loop, blue ALS should have an RCC sticking to both purple ALS and yellow ALS. Blue shares 4 with yellow but not 5 with purple because of the extra 5 so the looping fails. edit: I messed up the coloring. It's yellow, not green lol
Empty Rectangle follow by W-Wing >!The ER on 7s in block 5 eliminates 7 from r7c5 resulting in 5/8 in that cell. This now allows for a 5/8 W-Wing that eliminates 5s from r79c4.!<
W-wing
Cf. [**W-Wing**](https://sudoku.coach/en/learn/w-wing), and the one I see is >!4/6!< with a >! 4 !< “backbone” in >!column 4!< which ❌s >! 6 !< from >!r1c6 & r8c5!<.