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Jelly-Fish Strategy From sudokuwiki.org, the puzzle solver's site |

Jelly-Fish extends Swordfish one further row and column. We are looking for either- four rows such that,
*in total*, four cells are occupied in the row by a candidate number; or - four columns such that,
*in total*, four cells are occupied in the column by a candidate number
If this configuration is found then we can look in the opposite direction (if by row then down the column, if by column then across the row. If any candidates are found they can be eliminated. After the elimination both conditions above will hold. This diagram shows a full Jelly-Fish with four X found in four columns and aligned on four rows. It means we can remove any X found in the columns and it leaves behind a 4 by 4 grid. |
Jelly-Fish Diagram |

Finding exactly candidate X in all sixteen cells (a 4-4-4-4 formation) is extremely unlikely. But the logic of Jelly-Fish (and Sword-Fish) is that we only need four X in total over the four rows and columns. Here is a minimal spread of a particular candidate X - a 2-2-2-2 formation. Most of the time you will have a mixture of two, three or four candidates lined up. One way to double check the logic is to pretend any of the crossed out Xs is a solution. When you do that and trace the consequences you will find at least one row (or column) with no X left - clearly a bad consequence. |
Partial Jelly-Fish |

This is a real Jelly-Fish example, one of the very few I have that does actually show up in the solver. It is based on the candidate 2 and I have put a red box around the 2s that are part of the formation. The solver will highlight in yellow all the cells of the pattern whether they have a candidate 2 in them or not. The pattern establishes that we have 2 common to four rows (A,D,F and J) which are aligned on four columns (1,5,8 and 9). Therefore four 2s must go in those yellow cells. That precludes any other 2 in the columns - which are marked for removal (green cells). This is a 3-2-3-3 formation Jelly Fish. |
Example jelly-Fish: Load Example or : From the Start |

I am pleased to report a massive catch by Klaus Brenner from Germany. He has created a 31 clue Sudoku with a required JellyFish containing an amazing 18 eliminations. Well done Klaus! 8th October 2012 |
18 elimination Jelly-Fish: From the Start |