Hmm I don't get what you mean. For a valid sudoku there shouldn't be any guessing involved? So during any stage of solution, there should be always a single move that is the only option option move solution forward?
But even then humans do "moves" like "if i put that number here then that eliminates all other possibilities, that leaves us only that other number", which is kinda like guessing. So even if there are no single so human also tries if a valid move will block all future valid moves. A brute force algorithm does just that, except that it has a much larger memory and computation speed so it can think that at 9x9 depth to find a perfect solution
> For a valid sudoku there shouldn't be any guessing involved?
In the philosophy presented on that channel, it's not that such a Sudoku puzzle is "invalid," it's just not particularly interesting or 'beautiful'.
From my viewing, there appear to be two differences between "logic" and "guessing" (or "bifurcation"):
* Bifurcation/guessing is just as happy with a correct guess as an incorrect one. If I guess that a square is a '1' and then fill out the rest of the puzzle without finding a contradiction, then that's a good (in fact the best!) guess. "Logic," on the other hand, seeks contradictions to rule out possibilities
* "Guessing" is content to proceed arbitrarily far down the solution tree to find a solution (or contradiction), whereas "logic" limits itself to a few steps that can stay in a human's working memory.
However, the difference is clearer with the kinds of puzzles highlighted on the linked channel. These puzzles often include additional constraints, such as "the first three cells in the row form an increasing/decreasing sequence." "Logic" then provides universal derived constraints (such as "a 9/1 can never be in the middle of this sequence") that are more obviously distinct from depth-first-search guessing.
I've never understood the difference. When I solve sudokus, including this one, I use backtracking all the time. "The 2 goes here or here, if it goes here then I get a 2 here, a 2 here and there's no room for the 6 there...so the 2 goes in the other spot after all". The "forward methods" are equivalent: just shortcuts to the same thing, spotting reusable patterns like the "ringing the domino" motif the solver identifies in the video.
The human techniques are all about forward actions only, never guesses.