Today's Dragon Tip
With version 4.0, Sudoku Dragon now supports the Alternate Pair strategy, letting it spot and explain the use of X-Wing and Swordfish in any Sudoku puzzle.
Coloring Sudoku Squares [Page 11 of 15])
To keep track of squares on paper and pencil is easy, you can mark a square and rub it out when no longer needed. Sudoku Dragon offers color marking that lets you easily put a temporary mark on a square. There is a command to quickly clear coloring from all squares in one go.
The colors are added from the right mouse menu or the Edit menu or, using the keyboard SHIFT+Function key.
In this example puzzle screenshot, coloring has been used to identify squares that can take a 5. Alternate pairs have been marked with different square colors. Starting with orange square Bg this is paired to turquoise square Hg. Only one of these two squares can be the '5' in column g. Next Hg is paired to orange square Ii as a pair in region Gg. This square is in turn paired with turquoise square If. In addition there is another pair Bd (blue) and Fd (red) in column d. Having marked the alternate pairs it is evident that square Bf (lime green) can not take a 5 as it is in the same column as a turquoise square and the same row as an orange square. If the orange squares are correct then Bf can not take a 5 but nor can it if the turquoise squares are correct. As either orange or turquoise must be correct and not both must be correct that proves it!
You can use coloring just to remember particular interesting squares. Together with the square annotations coloring is a useful feature.
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