Swordfish: extend fish logic to three lines
A Swordfish uses one digit across three base rows whose candidates all fall within the same three cover columns.
Key idea
The three base rows must place the digit in the three cover columns, so outside candidates in those columns are impossible.
See the move, step by step
Trace candidate 7 through rows 1, 3, and 7.
Step 1 of 4
Filter for a single digit
Compare rows where candidate 7 appears only two or three times.
Step 2 of 4
Confirm three cover columns
Every 7 in the base rows lies in columns 1, 3, or 6. Each cover column participates in the pattern.
Step 3 of 4
Clear outside cover candidates
Remove 7 from R5C1, R8C3, and R8C6 because they lie in cover columns outside the base rows.
Step 4 of 4
Leave the fish unresolved
The base candidates remain possible; only the cover-column outsiders are removed.
Try it on today's puzzle
After learning X-Wing, scan the same way for three rows whose candidate positions use no more than three columns.
Play today