Exploring Sudoku

I have one Sudoku tactic that I have not seen described.

If you have four unknown cells that form a rectangle and three of them can only be "x" or "y", then the last one cannot be either "x" or "y".

The logic behind this is a bit subtle.  Any puzzle submitted for play must have one and only one solution.  Any rectangle of the form x/y/y/x is exactly equivalent to the rectangle y/x/x/y.

Have fun!

Well, I have come across puzzles with more than one solution.  My preferred solution method is to come up with pairs of cells (in a square, row, or column) that can only have two values.  Occasionally, I can get to the point where all that is left are multiple pairs of these cells, and either solution is valid.  During the sudoku tournament at the AG, the organizer mentioned this can happen for some puzzles.  

I have one Sudoku tactic that I have not seen described.

If you have four unknown cells that form a rectangle and three of them can only be "x" or "y", then the last one cannot be either "x" or "y".

The logic behind this is a bit subtle.  Any puzzle submitted for play must have one and only one solution.  Any rectangle of the form x/y/y/x is exactly equivalent to the rectangle y/x/x/y.

Have fun!

Well, I have come across puzzles with more than one solution.  My preferred solution method is to come up with pairs of cells (in a square, row, or column) that can only have two values.  Occasionally, I can get to the point where all that is left are multiple pairs of these cells, and either solution is valid.  During the sudoku tournament at the AG, the organizer mentioned this can happen for some puzzles.  

I have one Sudoku tactic that I have not seen described.

If you have four unknown cells that form a rectangle and three of them can only be "x" or "y", then the last one cannot be either "x" or "y".

The logic behind this is a bit subtle.  Any puzzle submitted for play must have one and only one solution.  Any rectangle of the form x/y/y/x is exactly equivalent to the rectangle y/x/x/y.

Have fun!

Sounds like an arbitrary rule. But life is full of many of those.

Well, I have come across puzzles with more than one solution.  My preferred solution method is to come up with pairs of cells (in a square, row, or column) that can only have two values.  Occasionally, I can get to the point where all that is left are multiple pairs of these cells, and either solution is valid.  During the sudoku tournament at the AG, the organizer mentioned this can happen for some puzzles.  

I have one Sudoku tactic that I have not seen described.

If you have four unknown cells that form a rectangle and three of them can only be "x" or "y", then the last one cannot be either "x" or "y".

The logic behind this is a bit subtle.  Any puzzle submitted for play must have one and only one solution.  Any rectangle of the form x/y/y/x is exactly equivalent to the rectangle y/x/x/y.

Have fun!

Sounds like an arbitrary rule. But life is full of many of those.

Well, I have come across puzzles with more than one solution.  My preferred solution method is to come up with pairs of cells (in a square, row, or column) that can only have two values.  Occasionally, I can get to the point where all that is left are multiple pairs of these cells, and either solution is valid.  During the sudoku tournament at the AG, the organizer mentioned this can happen for some puzzles.  

I have one Sudoku tactic that I have not seen described.

If you have four unknown cells that form a rectangle and three of them can only be "x" or "y", then the last one cannot be either "x" or "y".

The logic behind this is a bit subtle.  Any puzzle submitted for play must have one and only one solution.  Any rectangle of the form x/y/y/x is exactly equivalent to the rectangle y/x/x/y.

Have fun!

Well, I have come across puzzles with more than one solution.  My preferred solution method is to come up with pairs of cells (in a square, row, or column) that can only have two values.  Occasionally, I can get to the point where all that is left are multiple pairs of these cells, and either solution is valid.  During the sudoku tournament at the AG, the organizer mentioned this can happen for some puzzles.  

I have one Sudoku tactic that I have not seen described.

If you have four unknown cells that form a rectangle and three of them can only be "x" or "y", then the last one cannot be either "x" or "y".

The logic behind this is a bit subtle.  Any puzzle submitted for play must have one and only one solution.  Any rectangle of the form x/y/y/x is exactly equivalent to the rectangle y/x/x/y.

Have fun!