Antiknight Phistomefel

[Raumplaner]

Hi there PotatoHead21,

I can easily follow your logic and think it's a very nice observation. Many thanks for sharing.

In any anti-knight sudoku, there must be at least 8 unique digits in the Phistomefel Ring. This can be proven using the above image.

If a digit is not present in the Phistomefel Ring, it must either go in the blue pedals or the green pedals. Either way, that digit always gets ruled out of the pink cells in row 5 and column 5. That means in row 5, that digit must go in box 5 and in column 5, that digit must also go in box 5, which places it in the central cell in the grid (marked in purple).

That also means you can't have more than one digit missing from the Phistomefel Ring in an anti-knight puzzle because both of those digits would have to be placed in r5c5.