A Swordfish is an X-Wing stretched to three rows and three columns. A digit's remaining candidates, across three rows, all fall within the same three columns — not necessarily one candidate per row per column, just that collectively they never leave those three columns. That's enough to eliminate the digit from the rest of those columns.
Between them, the three rows must place the digit somewhere in those three columns — and since each column can only hold the digit once, the three rows exactly use up the three columns. No other row can still place that digit in any of them.
In rows 1, 3, 6, 4 can only go in columns 1, 2, 7. The cells form a three-row pattern.
Each of the three rows must place the digit in one of these columns, and each column can only take it once, so those columns are used up by these rows.
4 can be crossed out of the other cells in columns 1, 2, 7.
KaizenDoku spots every one of these patterns automatically after each game, and shows you exactly where you used them on your own board.
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