Sudoku-YAdvanced
Swordfish: one digit across three rows
Swordfish extends the X-Wing idea to three units. It need not form a filled rectangle or contain nine candidate positions.
Practise on a board ↓LOOK · TRY · UNDERSTAND
Try it and see why
Three rows: which columns?
Rows A, D and G have no placed 6. Their only spots for it are A2/A5, D5/D8 and G2/G8. Only the digit we are tracking is displayed here. A lone small digit is not a Single.
Our own partial teaching board, not a full puzzle. Large digits are placed values; small digits are candidates. Dots mean the cell is not described here. Complete candidate lists are part of the stated scenario, not calculated from the dots.
A uses column 2 or 5. That alone is not enough; check the other rows.
Green outline = evidence · Purple “try” = an assumption · Crossed out = removed candidate
Follow one row at a time. Can you remove candidates at B2, E5 and H8?
Select a cell, then tap a candidate below.
Look at all the evidence first, then try the eliminations.
See the reasoning
A, D and G each need one 6 without repeating a column. They use all of columns 2, 5 and 8. Remove 6 at B2, E5 and H8, keeping the source cells.
Digit set 1/9 · A different digit set in the same pattern, not a new full puzzle.
Read the source principles: HoDoKu — Basic Fish
Three restricted source rows
For a digit missing from three rows, if all its positions across those rows occupy just three columns, those columns are reserved. Remove that digit outside the source rows in the three columns. The column-based version reverses the roles.
HoDoKu — Basic Fish · SudokuWiki — Swordfish
Crossed-out digits are eliminations. Check the full conditions in the worked example below.
Six positions for digit 6
Let row A permit 6 only at A2/A5, row D at D5/D8 and row G at G2/G8. Their 6s must use columns 2, 5 and 8 without repeating a column. Remove 6 from B2, E5 and H8.
Try before revealing
What if A9 also allows 6?
Show explanation
The original basic Swordfish no longer holds: there is a fourth possible column. Do not ignore the extra position.
Preserve the source candidates
The sources reserve places for the digit. Targets lie outside them in the crossing units. Other digits in a source cell do not invalidate the fish; the pattern tracks just one digit.
Scanner coverage
The game detects basic row- and column-based Swordfish with two or three positions per source unit. Finned and more complex fish are not included. An empty result does not establish that every possible technique has been exhausted.
References and further reading
Read the source explanations and compare them with our examples. Links are references, not endorsements or claims of affiliation.