The XY-Wing technique involves three cells, and each of them has two candidate digits. Below, we will use a real Sudoku puzzle to demonstrate the Block-Column pattern of this technique as an example.
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In this puzzle, the pink cell (R8,C5) and the two yellow cells (R7,C6) and (R6,C5) each have two candidate digits. The yellow cell (R7,C6) shares the same 3x3 block B8 with the pink cell, and they have a candidate digit 8 in common. The other yellow cell (R6,C5) shares the same column C5 with the pink cell, and they have a candidate digit 4 in common. Also, the two yellow cells have a common candidate digit 3. These three cells form an XY-Wing (Block-Column) pattern.
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There are two possibilities for the pink cell:
So in either case, the orange cells cannot be 3. The candidate digit 3's in the orange cells can be removed, as shown in Figure 2.