sudokUI › Sudoku techniques › Sashimi X-Wing
Sashimi X-Wing in sudoku
Two rows (or columns) have candidate X at three corners of a rectangle, and their only other candidates for X, the fins, all lie in the missing corner's box.
Why it works
If no fin is true, both columns get their X from the two rows; if one is, its box holds no other X. Cells of those columns in the fin box, outside the two rows, lose X, or likewise with rows and columns swapped.
How to spot it
Look for an X-Wing with one corner missing, where the gap's row or column has its other candidates for X inside the gap's box.
Worked example
Sashimi X-Wing on 1: in columns 4, 8, 1 sits in rows 6, 9 (r6c4, r6c8, r9c8) except for the fins r7c4, r8c4. Either the fins are false and the fish holds, or a fin is true; a 1 that sees every fin and lies in the cover rows outside the base is false both ways. So 1 is removed from r9c6.
Practise it on a real puzzle. sudokUI generates a puzzle that needs Sashimi X-Wing and takes you straight to the position where it applies. Hints draw the pattern on the board and explain the step.
In a puzzle's rating
Each time the solver needs Sashimi X-Wing, the puzzle's difficulty rating grows by 150. Its class is Hard. It is needed in 1 in 260 puzzles that sudokUI generates. How the rating works.
More finned fish
Finned X-Wing · Finned Swordfish · Sashimi Swordfish · Finned Jellyfish · Sashimi Jellyfish