LogFAQs > #962552579

Serious Cat posted...

I think it's the other way around: it's a double jellyfish (or a pair of x-wings plus the knight's move and diagonal restraints) keeping the digit out of the forbidden zone in your puzzle. Under normal sudoku rules, there's nothing keeping any specific digit out of the ring.

https://gamefaqs.gamespot.com/a/user_image/6/6/4/AAPWHiAAC59A.jpg
Edit because examples of a workable ring probably should be workable.

It's knights and bishops that causes the ring in my puzzle, but the ring excluding the 4 corners could be proven by the same logic on the normal ring as you showed in your example:
https://gamefaqs.gamespot.com/a/user_image/5/7/8/AACZqoAAC6a6.png

Black must appear once in the blue column, once in the red column, once in the yellow column, and once in the green column, same for once in each colored row, thus black has to appear 8 times in addition to it's appearance in the center, and so Phistomaphel is proven via jellyfish and not SET.