Easy Proof of Tough? for March 24, 2007

The following is an illustrated proof for the Tough Sudoku of March 24, 2007. This is a very easy puzzle, and only requires one to know one technique, Coloring.

You should not need to refer to previous blog pages to understand this proof. Links to these pages are found to the right, under Sudoku Techniques.

This illustration, shows only the one step one may need to unlock the puzzle.

Puzzle at start

Some Unique Possibilities are available here.

Find them shown on the next illustration.

Possibility matrix at UP 27

Above find the current possibility matrix. At this point there are many steps possible. While scanning for possible easy eliminations, I found the following situation on 2s:

Locations for 2s at UP 27

There are a few easy coloring eliminations available with the 2s. I will illustrate two of them. One only needs to find one.

Coloring on 2s

Above, i5=2 => i7≠2 & h46≠2

i5≠2 => e5=2 => e9≠2 => h9=2 => i7≠2 & h46≠2

After making these eliminations, the puzzle is reduced to a cascade of Unique Possibilities to the end.

Coloring on 2s alternate

Above is an alternate approach, commonly called a two string kite.

Again, the puzzle reduces to Unique Possibilities after i5≠2

Probably, this puzzle is a bit too easy for a tough! My rating system would rate this puzzle: .03