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Sashimi Jellyfish in sudoku

Unfair · rating cost 260 · Finned Fish · also called Sashimi Finned Jellyfish, Finned Sashimi Jellyfish

Four rows (or columns) have candidate X only in four shared columns (or rows) plus fins, extra cells in one box, and a finned row has only one non-fin candidate.

Why it works

If no fin is true, all four columns get their X from the four rows; if one is, its box holds no other X. Cells of those columns in the fin box, outside the four rows, lose X, or likewise with rows and columns swapped.

How to spot it

Find four rows fitting four columns where one row has a single non-fin candidate and its extras lie in one box crossed by another column.

Worked example

Sashimi Jellyfish example on a sudoku board. Sashimi Jellyfish on 6: in rows 3, 4, 7, 8, 6 sits in columns 1, 2, 4, 9 (r3c1, r4c2, r4c4, r7c2, r7c9, r8c1, r8c9) except for the fin r3c6. Either the fin is false and the fish holds, or the fin is true; a 6 that sees every fin and lies in the cover columns outside the base is false both ways. So 6 is removed from r1c4. — remove base rows: the 6s of the fish cover columns: where the base's 6s must land fin: 6s outside the fish, in one box; a removal must see every fin

Sashimi Jellyfish on 6: in rows 3, 4, 7, 8, 6 sits in columns 1, 2, 4, 9 (r3c1, r4c2, r4c4, r7c2, r7c9, r8c1, r8c9) except for the fin r3c6. Either the fin is false and the fish holds, or the fin is true; a 6 that sees every fin and lies in the cover columns outside the base is false both ways. So 6 is removed from r1c4.

Step 35 of this puzzle's solution, found and verified by the sudokUI engine. Cells are named by row and column: r2c3 is row 2, column 3. Play this puzzle from the start.

Practise it on a real puzzle. sudokUI generates a puzzle that needs Sashimi Jellyfish and takes you straight to the position where it applies. Hints draw the pattern on the board and explain the step.

Practice Sashimi Jellyfish Open in the app's guide

In a puzzle's rating

Each time the solver needs Sashimi Jellyfish, the puzzle's difficulty rating grows by 260. Its class is Unfair. It is needed in 1 in 7,200 puzzles that sudokUI generates. How the rating works.

More finned fish

Finned X-Wing · Sashimi X-Wing · Finned Swordfish · Sashimi Swordfish · Finned Jellyfish

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