Can you believe how quickly summer left us at the River? Good thing we have Sudoku to keep our minds sharp through the off-season.

### Clueless?

We start with a Sudoku puzzle in progress, where it appears that there are no more obvious or not-so-obvious clues. Can you find the hidden clue in Puzzle #122?

(The answer follows the conclusion of Puzzle #124, the feature puzzle for October)

### Logic Puzzle

Difficult rating … 4/10

(Rating based on puzzles not requiring advanced techniques)

Puzzle #123 should present a moderate challenge!

## Feature Puzzle

Difficult rating … 4/10

(Rating based on puzzles requiring advanced techniques)

### PUZZLE PREPARATION

Prior to utilizing techniques 1-8, complete the 5 Steps of Puzzle Preparation …

**1. FILL IN DATA FROM OBSERVATIONS**

2. **FILL IN OBVIOUS ANSWERS**

3. **FILL IN NOT-SO-OBVIOUS ANSWERS**

4. **MARK UNSOLVED CELLS WITH OPTIONS THAT CANNOT EXIST IN THOSE CELLS**

5. **FILL IN THE OPTIONS FOR THE UNSOLVED CELLS**

The first thing we observe is that C9R9=8 & C8R7=9.

In box two, a 7 can only exist as an option in C5R2 & C5R3; therefore, a 7 cannot exist as an option in C5R5 & C5R6.

C1R4=2.

Now your grid should look like Example #124.1 below:

This completes Puzzle Preparation Steps 1-4. Next, we will fill in options for all unsolved cells, giving us Example #124.2 below:

Dan recommends the following Steps to complete the puzzle.

Step 1: Sudoku Pairs, Triplets and Quads – See September 2015

Step 2: Turbos & Interaction – See October 2015

Step 3: Sudoku Gordonian Rectangles and Polygons – See November 2015

Step 4: XY-Wings & XYZ Wings – See December 2015

Step 5: X-Wings – See January 2016

Step 6: DAN’S YES/NO CHALLENGE

Step 7: DAN’S CLOSE RELATIONSHIP CHALLENGE

Step 8: AN EXPANSION OF STEP 7. Steps 1-5 are relatively common techniques and are explained in the *TI LIFE* articles. Steps 6-Posts8 are covered in detail, in Dan’s book.

There are no Step-1-5 techniques hat can be further applied. Are there are any good Step 6 potentials. As in previous articles, we determined a particular number was a potential for a successful Step 6 exercise if that number appears as a given answer in 3 separate boxes, such that the boxes are not side-by-side, nor over each other. Which numbers do you see that are good candidates? Yes, the 5’s & 6’s.

We will start with the 5’s and perform a Step 6 exercise, Dan’s Yes-No Challenge”, per Example #124.3 below, using C3R1 & C9R1 as our starter cells highlighted in yellow.

Either C3R1 or C9R1 has to be a 5. First, we will assume C3R1=5 and mark it with a capital Y, for yes. Then we will mark the cells it affects with a Y or N, indicating a yes or no.

Next, we will assume C9R1=5, and mark it with a “y”. Then we will mark the cells it affects with a y or n.

We see that C5R6, C4R8 & C9R4 are marked N,n. It means that those cells cannot be a 5, regardless of which starter cell is a 5. The 5 can be eliminated as an option for those cells.

We also note that C4R4 is marked Y,y, which means this cell is a 5 regardless of which starter cell is a 5. So, C4R4=5

From this discovery, you are “off to the races”, and the puzzle leads to an easy conclusion, as per Example #124.4 below:

May the gentle winds of Sudoku be at your back.

By Dan LeKander, Wellesley Island

*Thought of the day* … a friend recently asked me regarding Sudoku, “have you always been good with numbers?” My reply was “yes, and I have always been good with letters, since you can perform Sudoku with letters A-I instead of numbers 1-9”. Of course, being proficient with Sudoku does not require any magical mastery of numbers or letters. It is purely a game of logic.

**Clue for Puzzle #122** … did you find the clue? If not, read on.

Check row 6. What do you see?

We see that C1R6 & C8R6 have options 5 & 6. That leaves C8R6=9.

You may want to continue and see if you can solve the puzzle!