How to Solve Sudoku: W-Wing

2 cells with the same notes {A,B}, joined by a column where A has only 2 places. Then B can be removed from any cell that sees both of the 2 cells.

On Puzzle Lounge it appears at Master.

See it step by step

  1. A board full of notes. Look at the cells with 2 notes (the small digits are the notes, or candidates)
  2. 2 cells with only 4 and 9 in their notes (far apart, and they do not see each other)
  3. In column 7, 4 has only 2 places (each end is seen by one of those cells)
  4. If 4 is here, this cell is 9 (it sees the cell holding 4, so it cannot be 4)
  5. If 4 is here, this cell is 9
  6. Either way, one of the 2 cells is 9
  7. So a 9 that sees both of the 2 cells can be removed (9 goes from row 3, column 2)

This is Master No.3, partly solved.

Solve this puzzle →

How to find it

  1. Among the cells with only 2 candidates, find a pair with the same 2 digits (that do not see each other).
  2. Find a row, column or box where one of those digits has only 2 places, with each end seen by one of the cells.
  3. See whether any cell that sees both of the 2 cells has the other digit as a candidate.

Things to watch

  • Each end of the connecting line must be seen by one of the 2 cells.
  • What you remove is the other digit, not the one used for the link.
Read the full explanation

When 2 cells apart from each other both have only {A, B} as candidates, and a row, column or box has only 2 places for A with each end seen by one of the cells, one of the 2 cells must be B. So B can be removed from any cell that sees both of the 2 cells.

Suppose 2 cells far apart both have {4, 9} as candidates. And a column has only 2 places for 4, one end seen by the first cell and the other by the second.

The column's 4 goes in one of its ends. A cell that sees the end holding 4 cannot be 4, so it is 9. So one of the 2 cells must be 9.

So 9 cannot go in any cell that sees both of the 2 cells.

Row 3, column 9 and row 5, column 2 are both {4, 9}. 4 can only go at row 1, column 7 or row 5, column 7, and the cell that sees it becomes 9. So 9 can be removed from the candidates at row 3, column 2, which sees both of the 2 cells.

Other techniques

Hidden SingleNaked SinglePointingClaimingHidden PairHidden TripleCage Combinations (Killer)Rule of 45 (Killer)Naked PairNaked TripleX-WingXY-WingSwordfishSkyscraper2-String KiteXYZ-WingJellyfish

For the basics and how to use notes, see how to solve sudoku, with tips. If you get stuck, the game's hints guide you step by step, starting with where to look.

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