The Empty Rectangles method is a strategy for solving Sudoku puzzles. I have seen the description of this strategy here, I have the following question:

Is there a problem if the other end of the strong link and the ERI intersect inside the box which contains the empty rectangle?

For example if, in the 4th picture of the link above, Y was in A2 and Z in A8.


1 Answer 1



An Empty Rectangle means that in a box, a particular number is restricted to one row and one column. In this example on the linked page, the 8 in the top-right box is either in row C or column 8.

Either X or Y contains an 8. If Y contains the 8, then Z cannot. If X contains the 8, then the 8 in the top-right box cannot be in row C, so it must be in column 8. Then, Z also cannot contain 8. This is why this configuration allows Z to be eliminated.

If Y was at A2 and Z at A8 instead, this logic would not eliminate Z. If X is 8, then the 8 in the top-right box would have to be in column 8, but A8 is still a possible position for it.


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