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I though that too at first but actually they seem well practiced too. Eg other sudoku-style puzzles also have knight move rules. The main trick I missed is the

I though that too at first but actually they seem well practiced too. Eg other sudoku-style puzzles also have knight move rules. The main trick I missed is the forking one (if I put a 3 here then it reaches here and here by knight’s move therefore it can’t go here). That said It is still impressive and I think practice is not sufficient to explain how fast he is at it.

ghusbands 6y ago
> (if I put a 3 here then it reaches here and here by knight’s move therefore it can’t go here) A possibly-simpler way to look at it is the inverse. Putting a 3 here or here (where it must go) both block this other place, so we know this other place is blocked either way.
- dan-robertson 6y ago
  Yes, that’s something I tried thinking about but computing the intersection of two or more quite large regions turns out to be harder than using the symmetry to only look at one region. There are also tricks one can learn for eg dominos.