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# Solving Techniques 13 XY-Chains

As shown below, there is a chain from the red cell’s [12] going to [23] [34] [14].

If C2 is [1], the result is as follows.

If C2 is [2], the result is as follows.

In either solution, 1 would not be in the overlapping area X.

This situation is known as an XY-chain.

## XY-Chains 2

This is another pattern. As seen below, [23], [34], [14] is linked to the red cell [12].

If B3 is [1], the result is as follows.

If B3 is [2], the result is as follows.

In either position of 1, 1 can’t be entered in the overlapping area X.

These are rarely seen in actual problems. However, when you are solving a very advanced problem and get stuck, it is a good technique to remember.

## XY-Chains 3

We made a slightly different pattern. As shown below, the red [12] is linked to [23][34][34][45][15].

If B3 is [1], the result is as follows.

If B3 is [2], the result is as follows.

In either position of 1, there can’t be 1’s in the overlapping area X.

## Names of cells in Sudoku

 A1 A2 A3 A4 A5 A6 A7 A8 A9 B1 B2 B3 B4 B5 B6 B7 B8 B9 C1 C2 C3 C4 C5 C6 C7 C8 C9 D1 D2 D3 D4 D5 D6 D7 D8 D9 E1 E2 E3 E4 E5 E6 E7 E8 E9 F1 F2 F3 F4 F5 F6 F7 F8 F9 G1 G2 G3 G4 G5 G6 G7 G8 G9 H1 H2 H3 H4 H5 H6 H7 H8 H9 I1 I2 I3 I4 I5 I6 I7 I8 I9