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Techniques · Expert
Jellyfish
The largest fish: a digit's places in four rows all fall within the same four columns, so the digit can be removed from the rest of those four columns. It also works with columns and rows swapped.
How to spot it
Very rare. It shows up when a digit is still missing from most of the board. List the rows where the digit has two to four places and look for four that share four columns.
Example
9
2
478
47
1
45
6
3
6
5
1
2
49
3
7
8
49
78
3
478
58
4679
469
2
1
459
78
6
789
14
5
47
19
3
2
5
14
2
19
3
79
6
47
8
3
14
79
6
8
2
19
5
47
124
8
3
49
1269
469
45
247
457
24
7
6
3
24
5
8
9
1
124
9
5
7
124
8
3
24
6
In columns 3, 4, 6 and 7, 4 can only go in rows 1, 3, 4 and 7, so 4 can be removed from the rest of rows 1, 3, 4 and 7 (Jellyfish).
the pattern cells that lose a candidate (crossed out)