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Swordfish

A Swordfish is the 3-row/3-column generalization of the X-Wing. If a digit has candidates in at most three cells across three different rows, and those candidates all fall within the same three columns, the digit can be eliminated from those columns outside the three rows.

Advanced

How to read the grids

  • Given - clues from the starting puzzle
  • Subject - cells the technique focuses on
  • Eliminated - candidates this technique removes
  • Candidate - pencil marks shown for reference

How to spot it

Pick a digit. Find three rows where the candidate appears in only two or three cells, and those candidate columns are a subset of the same three columns. Same logic applies swapping rows and columns.

Three rows lock the digit into three columns - eliminate elsewhere in those columns.

Worked example

Digit 2 appears across rows 1, 5, and 8 in columns 2, 5, and 9. Other cells in columns 2, 5, 9 (outside those rows) can no longer hold a 2.

Time to practice

Reading is half the work. Try a puzzle now and look for the techniques you just learned.