ExpertUsefulness: Very low
Jellyfish
The four-line fish. A candidate confined to four columns across four rows is eliminated from the rest of those columns.
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A four-line fish boxes the candidate into four columns.
patterneliminatesolved
How to spot it
- 1Find four rows where a candidate appears in two to four cells.
- 2Confirm all sit within the same four columns.
- 3Remove the candidate from the columns' other cells.
When to use
Almost never by hand — it appears only in extreme puzzles.
When not to
If you're reaching for a jellyfish, a forcing chain is usually faster.
Common mistake
Mis-tracking one of the sixteen possible positions and drawing a false pattern.