Neuer (?) Fund über Sudoku-Geometrie

[Phistomefel]

That is a really cool generalization and an elegant proof! It is a neat observation that one can show all of the fish techniques with this argument.
Thank you, Fred! :-)
I agree that the technique is not necessarily helpful in a classic sudoku. I tried to apply it to some of the Weekly Unsolvables, but it never seemed like I actually gained any useful information from it. I think it is rather a different perspective on a classic sudoku than an advanced technique. Still, it might be useful in a killer sudoku.