Swordfish

Hard

X-Wing extended to three rows/columns; the digit is eliminated from those columns in all other rows.

How It Works

When a digit appears in at most three columns across three rows, it can be eliminated from those three columns in all other rows.

Like X-Wing but for 3 rows/columns. Each row must have the candidate in 2 or 3 of the same columns. The digit is locked in those columns, so it can't appear there in other rows.

Example

78
4
68
26
3
27
915
1
23
35
45
89
24
67
57
26
91
46
57
248
3
248
2
36
1
3458
456
3458
79
468
58
7
568
246
9
14
1456
245
3
49
356
7
126
1238
12568
58
1268
39
5
27
348
124
6
2348
478
19
61
27
9
245
2348
23458
4578
248
39
84
235
7
1235
16
25
169
Key cells of the techniqueCells where elimination is appliedCandidate to be placedEliminated candidate (crossed out)

Practice with a Real Puzzle

This 9×9 puzzle is solver-verified to require this technique on its solution path.

Medium26 givens