Sudoku

W-Wing practice

A W-Wing is two cells that hold the same two candidates, X and Y, and do not see each other. They are joined by a link: a row, column or box where X fits in only two cells, with one end seen by each of the pair.

X has to sit at one end of the link, which stops the cell seeing that end from being X. So at least one of the pair is Y, and Y can be crossed off every cell that sees both of them.

Row 5 can only take its 4 in the two yellow cells, so one of the blue cells is not 4 and must be 7. The 7 comes off the red cells, which see both blue cells.

How to spot a W-Wing

Find two identical two-candidate cells in different rows, columns and boxes. Then look for a unit where one of their numbers has only two places left, lined up with the pair.

Practise it on this page

The board above deals positions where the W-Wing is the only way forward, with every pencil note filled in. Cross off the candidates it rules out and press Next. Press Hint to see the pattern marked on the board.

In a full game, Master is the first level that can ask for it.