Sudoku Tutorial
Unique Corners
This solving technique is based
on avoiding a deadly rectangle.

A deadly rectangle can only exist
in an invalid puzzle (multiple solutions).

The four yellow squares shown are close to becoming a deadly rectangle.  If the cell in r9c8 was a 1 or a 6,   then the deadly rectangle would exist.  Since it is known that this is a valid puzzle, a deadly rectangle is not possible.

Therefore the 1 and 6 can be eliminated from r9c8.


Tutorial Home

Comments?  Email me!