Decabit Software
Double Block Line

Double Block Line is similar to Block Line except... doubled! With this technique, two blocks and two lines are taken into account.

Consider the sudoku below.

4
4
4
4
4
4
8 6 5 2 3
4
4
4
4
4

In the left and right blocks, the value 4 can only exist in the cells marked with a small 4.

If a 4 exists in the top row of the left block, then there must be a 4 in the bottom row of the right block. Alternatively, if the bottom row of the left block contains a 4, then there must be a 4 in the top row of the right block.

Wherever the two 4s are, we know that the top and bottom rows of the center block cannot contain a 4. So we can remove 4 as a possible value for those cells.
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Last Updated: 12/14/2017 7:20:56 AM CST