Sudoku Tutorial |

X-wing |

X-wing explained: The 4's in row 2 are strongly linked. One must exist, the other cannot. Same with the 4's in row 8. The 4's in row 2 and row 8 must be diagonally opposed. (A 4 in row 2 will eliminate the 4 in row 8) These are the only two possibilities. Either way, candidate 4 is now committed in columns 3 and 6. Any 4's in the other cells of those columns can be eliminated Another way to say this is that the 4's within the columns become strongly linked. In column 6, there are five 4's. Any pair of those 4's is weakly linked. That is until you find the X-wing. The X-wing creates a strong link between the 4's in r2c6 and r8c6 (the yellow squares in column 6). This strong link means that you can now eliminate the 4's in the other cells of that column. (back) |

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