[upd]: Sudoku 129

If you are using Sudoku129 materials for practice, experts recommend several techniques: How to play Sudoku

Two cells in a row/column/box that can only contain the same two numbers (e.g., a 2 or 7). Therefore, those numbers can be eliminated from other cells in that unit. sudoku 129

The difficulty of a puzzle is not just about its label. Frame Sudoku puzzles, for example, can be incredibly challenging because they often lack internal starting digits (known as "gimmies"). The Consecutive Sandwich Sudoku (#129) is a highly complex variant that often requires advanced logic. The variation is key: a puzzle numbered 129 in one series could be a gentle introduction, while in another series, it might be a brain-bending challenge designed for experts. If you are using Sudoku129 materials for practice,

If you notice that two squares within the same row, column, or box contain the exact same pair of candidate numbers (for example, both cells only have the options [2, 7] ), you have found a Naked Pair. While you do not know which square is 2 and which is 7, you know with absolute certainty that those two numbers must occupy those two cells. Therefore, you can safely eliminate 2 and 7 from the candidate lists of all other cells in that same row, column, or box. The same logic applies to Naked Triples (three cells sharing three candidates). Pointing Pairs Frame Sudoku puzzles, for example, can be incredibly