Block & Row/Column Interaction

This is where you can remove a number as a possibility in certain squares by examining how a block interacts with either a row or column. Consider the following board:

In the first block, a 7 can only go in either of the two highlighted cells.  Because both of these cells are in the same block and row, we know that a 7 must be in row two in block one. Therefore, since we know a 7 must be in row two, we can eliminate 7 as a possibility from the rest of row two.

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