X-Wing

A digit is confined to the same two columns in two rows (or the same two rows in two columns).

A technique for Hard puzzles. Play a Hard puzzle

What it does

Pick a digit, say 4. If in two rows the 4 can go in only two cells each, and those cells sit in the same two columns, then the two 4s of those rows are in those columns: one in each, at opposite corners of a rectangle. Either way, both columns get their 4 from these two rows.

How to spot it

Choose one digit and look along the rows for those where it has exactly two places. When two such rows have their two places in the same two columns, you have an X-Wing. The same works the other way round, with two columns and two rows.

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Blue: where 6 can go in the base lines (grey). Pink: the lines that lose 6.In rows 6 and 7, 6 can only go in the blue cells, which line up in columns 2 and 5. Whichever way it goes, columns 2 and 5 get their 6 there, so it can’t go anywhere else in them.It removes 6 from row 9, column 5.

What it lets you do

You remove the digit from every other cell of those two columns (or rows, if you started from columns). It often opens up a single somewhere in them.

Try it

Find the X-Wing on this board. Pick the cells it clears, mark the candidates it removes, then check.

These are the notes after the easier steps: some candidates are already removed, as they would be in your game.

Practise it

The best way to learn a technique is to meet it in a real game. Practice puzzles are sure to need it, at Hard level; any Hard puzzle may need it too.

Practise with real puzzles Play a fresh Hard puzzle