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How Sudoku X Breaks Symmetries
From sudokuwiki.org, the puzzle solver's site
It is an interesting question how a puzzle like the one illustrated here can have one solution. All the clues are stacked in the bottom half of the board with just one number in the middle row in E9. This puzzle is the first in a list of 12 clue puzzles published on sudocue.net. They are interesting both as very minimal puzzles (minimal clues) and for how they highlight just how different Sudoku X can be from normal Sudoku.
Sudoku X has two extra constraints in the diagonals - which must be filled with 1 to 9. Almost all Sudoku strategies can be applied to X and extended to take advantage of the diagonals as I wrote in this article. There are pitfalls, especially with patterns that require rectangles and specific combinations of rows, boxes and columns, as I also point out.
12 Clue Sudoku X: Load Example