> 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," i

> 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. The latter point is certainly fuzzy, and it leads to developing some heuristics (such as https://www.sudokuoftheday.com/techniques/hidden-pairs-triples/ https://www.sudokuoftheday.com/techniques/hidden-pairs-tripl... or https://www.learn-sudoku.com/x-wing.html https://www.learn-sudoku.com/x-wing.html) to reduce more complicated deductive chains into "single steps." 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.