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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.

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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

A1A2A3A4A5A6A7A8A9
B1B2B3B4B5B6B7B8B9
C1C2C3C4C5C6C7C8C9
D1D2D3D4D5D6D7D8D9
E1E2E3E4E5E6E7E8E9
F1F2F3F4F5F6F7F8F9
G1G2G3G4G5G6G7G8G9
H1H2H3H4H5H6H7H8H9
I1I2I3I4I5I6I7I8I9

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