The pattern of the Swordfish technique can appear in rows or in columns.
If a digit is a candidate in not more than three cells in each of three certain rows and the positions of all these cells are limited to three columns, then this digit will occupy one of the cells in those three columns in such three rows, and the position of this digit in each of those three columns will be in one of such three rows. As a consequence, this digit cannot be a candidate for other cells in those three columns. The following is an example to demonstrate this technique.
2
5
9
1
5
9
1
2
2
3
5
2
3
4
9
1
2
3
4
2
5
8
9
1
2
5
6
2
5
1
2
5
6
1
2
9
2
8
9
1
8
1
2
3
1
2
3
1
2
3
8
3
4
5
6
3
5
3
4
6
1
5
8
1
6
3
8
2
9
2
4
9
2
4
9
5
6
7
5
7
5
6
2
3
5
6
9
5
9
2
8
5
6
9
1
3
1
3
8
2
3
8
9
3
8
9
2
3
7
2
3
6
9
3
9
2
3
6
7
1
2
9
1
2
8
9
2
4
5
7
9
2
3
4
5
7
9
2
5
8
9
1
2
4
5
7
9
2
3
4
5
7
9
1
2
5
9
1
2
3
9
1
2
3
9
2
3
5
9
2
3
4
5
9
1
3
1
2
3
4
5
9
In the three rows R2, R6, and R7 of the puzzle above, the cells that contain the candidate digit 3 are highlighted in green. Notice that each of these three rows has no more than three green cells, and all these cells are limited to three columns C1, C7, and C9. These green cells in the three rows form a Swordfish in rows pattern.
2
5
9
1
5
9
1
2
2
3
5
2
3
4
9
1
2
3
4
2
5
8
9
1
2
5
6
2
5
1
2
5
6
1
2
9
2
8
9
1
8
1
2
3
1
2
3
1
2
3
8
3
4
5
6
3
5
3
4
6
1
5
8
1
6
3
8
2
9
2
4
9
2
4
9
5
6
7
5
7
5
6
2
3
5
6
9
5
9
2
8
5
6
9
1
3
1
3
8
2
3
8
9
3
8
9
2
3
7
2
3
6
9
3
9
2
3
6
7
1
2
9
1
2
8
9
2
4
5
7
9
2
3
4
5
7
9
2
5
8
9
1
2
4
5
7
9
2
3
4
5
7
9
1
2
5
9
1
2
3
9
1
2
3
9
2
3
5
9
2
3
4
5
9
1
3
1
2
3
4
5
9
The positions of the digit 3 in the three rows R2, R6, and R7 are limited to three columns C1, C7, and C9. Consequently, in these three columns C1, C7, and C9, the digit 3 must also be in one of the green cells in rows R2, R6, or R7, but not others. So, if the digit 3 appears in other cells as a candidate in columns C1, C7, and C9 (those candidate 3's in the orange cells), they can be removed as shown in Figure 1b.
The roles of rows and columns are exchangeable for this technique. The following is an example for Swordfish in columns.
2
6
9
2
6
9
6
9
5
6
1
6
5
6
7
1
6
7
1
5
9
1
2
5
3
9
1
3
5
9
1
2
3
5
3
9
6
9
3
6
3
9
6
9
6
7
3
6
7
3
4
3
4
5
3
5
3
6
9
3
6
9
6
9
5
6
7
9
5
6
7
6
7
9
3
6
7
3
6
6
7
3
4
9
3
4
9
3
6
7
1
3
9
1
3
6
In the three columns C2, C4, and C7 of the puzzle above, the cells that contain the candidate digit 9 are highlighted in green. Notice that each of these three columns has no more than three green cells (actually, in this case, only two cells in each column), and all these cells are limited to three rows R3, R7, and R8. These green cells in the three columns form a Swordfish in columns pattern.
2
6
9
2
6
9
6
9
5
6
1
6
5
6
7
1
6
7
1
5
9
1
2
5
3
9
1
3
5
9
1
2
3
5
3
9
6
9
3
6
3
9
6
9
6
7
3
6
7
3
4
3
4
5
3
5
3
6
9
3
6
9
6
9
5
6
7
9
5
6
7
6
7
9
3
6
7
3
6
6
7
3
4
9
3
4
9
3
6
7
1
3
9
1
3
6
The positions of the digit 9 in the three columns C2, C4, and C7 are limited to three rows R3, R7, and R8. Consequently, in these three rows R3, R7, and R8, the digit 9 must also be in one of the green cells in columns C2, C4, and C7, but not others. So, if the digit 9 appears in other cells as a candidate in rows R3, R7, and R8 (those candidate 9's in the orange cells), they can be removed, as shown in Figure 2b.