# Sudoku Puzzle 89, & 88 is a Doozy

### By: Dan LeKander

Volume 16, Issue 8, August 2021

Hope you are enjoying your summer and you are ready for a Sudoku challenge!

### Clueless?

As a bonus each month this year we will start with a Sudoku puzzle in progress, where it appears there are no more obvious or not-so-obvious clues. Does this puzzle #88 have any more clues? If you answered “yes” you are absolutely correct.

The other day I was thinking about this puzzle, trying to find the right word to describe this clue.  Somehow the word “doozy” came to mind. So, before calling this particular clue a doozy, I figured that I better check the official meaning of the word (and how to spell it). One online reference said a doozy is “Some-thing remarkable or exceptional, either positively or negatively, when compared to other in-stances of it”.  How true for this clue!

Be sure to find this clue yourself, as it will become another important tool in your Sudoku bag.

(The answer follows below after the conclusion of Puzzle #89, the feature puzzle for August)

## Feature Puzzle

The “Impossible” Series continues with Puzzle #89 …

DAN’S 8-STEP APPROACH TO SOLVING ALL SUDOKU PUZZLES

Once you have  completed the puzzle, to the extent that you have filled-in all obvious  answers and have written all potential options across the top of the  unsolved cells (PUZZLE PREPARATION), 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 7Steps  1-5 are relatively common techniques and are explained in the TI LIFE  articles above. Steps 6-8 are covered in detail, in Dan’s book.

### PUZZLE PREPARATION

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

1. FILL IN DATA FROM OBSERVATIONS
4. MARK UNSOLVED CELLS WITH OPTIONS THAT CANNOT EXIST IN THOSE CELLS
5. FILL IN THE OPTIONS FOR THE UNSOLVED CELLS

We will complete all of the first 4 steps in the order we observe them, until we conclude all Puzzle Preparation Step 1-4 clues.

The first thing we observe is that C5R6=7 & C3R7=9.

In box 9 a 1 can only exist as an option in C8R8 or C8R9; therefore, a 1 cannot exist as an option in C8R1 or C8R3.  Indicate this by placing a small 1 in the bottom of those two cells.

In box 3 a 4 can only exist as an option in C7R1 or C8R1; therefore, a 4 cannot exist as an option in C1R1, C2R1 and C3R1.

In box 3 a 7 can only exist as an option in  C7R3 or C8R3; therefore, a 7 cannot exist as an option in C2R3 or C3R3.

In box 7 a 3 can only exist as an option in C1R7 or C1R9; therefore, a 3 cannot exist as an option in C1R1, C1R2, C1R4 and C1R6.

In box 7 a 5 can only exist as an option in C2R8 or C3R8; therefore, a 5 cannot exist as an op-tion in C4R8, C5R8, C7R8 or C8R8.

In column 6 the options 6 & 8 can only exist in C6R3 and C6R7; so, enter those options at the top of those cells.

In box 5 a 9 can only exist as an option in C6R4 or C6R6; therefore, a 9 cannot exist as an op-tion in C6R2 and C6R9.

Now your grid should look like Example #89.1 below:

This completes puzzle preparation, so we will fill in the options for the unsolved cells, giving us Example #89.2 below:

There are no other Step 1-5 clues.

We will now proceed to Step 6:  Dan’s Yes-No Challenge.  We will start by searching the 1’s to see if there is a potential Step 6 clue, and then navigate through the 2-9’s.

There are 3 circumstances that establish the potential for a Step 6 exercise:

1. Look for just 2 unsolved cells in a box that contain the same option where these 2 cells are not in the same row or column.
2. Look for just 2 unsolved cells in a column that contain the same option where these 2 cells are not in the same box.
3. Look for just 2 unsolved cells in a row that contain the same option where these 2 cells are not in the same box.

In Example #89.3 below we will choose an 8 in C5R1 and C6R3 to perform this Step 6 exercise:

In box 2 either C5R1 or C6R3 is an 8.  We will first assume C5R1 is an 8 and mark it as “Y” to    indicate “yes”.   We will then indicate in cells with an 8 as an option as to whether they are a yes or no.   We will mark C6R3 with a small case “y” and perform the same exercise.  Each of the cells with a N,n designation means that these cells cannot be an 8 regardless of whether C5R1 or C6R3 is actually an 8, and the 8 can be removed as an option from these cells, giving us Example #89.4 below:

We can clearly see that C6R7=6, C6R3=8,  C7R5=8, and so forth, leading to an easy conclusion per Example #89.5 below:

May the gentle winds of Sudoku be at your back.

Dan LeKander

Clue for Puzzle #88 … focus your attention on row 9.   What do you observe?
We can see that C9R9 cannot be a 5.   We can see that C4R9, C5R9 & C6R9 cannot be a 5.  Therefore, C1R9 or C3R9 must be a 5.  This tells us that C2R8 cannot be a 5.   Since the only two choices for C2R8 are a 4 or 5, we conclude C2R8=4.  Then C2R7= 6, and so on.

Editor's Note:  Summer 2021!

Dan, when not out fishing, and his proofreader (and, as they say, better half) Peggy, give us a new challenge each month.

It was back in January 2016, when we published a final article in Dan's Series of Steps to learn the logic of Sudoku –  he asked if we would like a puzzle to solve every month … this editor said an enthusiastic… Yes, please!

If you have not already done so, I suggest you purchase Dan’s book: “3 Advanced Sudoku Techniques, That Will Change Your Game Forever!” Purchase of a book includes a 50-page blank grid pad, 33 black and two green tokens, to assist with Step 6.…

I also encourage you to write to Dan and tell him how his system is helpful!

The book is available online at ebay.com.

Be sure to read the TI Life's review of Dan's book by Jesse Kahn published in Jun 2015.

Here are links to all past Sudoku Puzzle Challenge beginning: February 2016, March 2016, April 2016, May 2016, June 2016, July 2016, August 2016, September 2016, October 2016, November 2016, December 2016, January 2017, February 2017, March 2017, April 2017, May 2017, June 2017, July 2017, August 2017, September 2017, October 2017, November 2017, December 2017, January 2018, February 2018, March 2018, April 2018, May 2018, June 2018, July 2018, August 2018, September 2018, October 2018, November 2018, December 2018, January 2019, February 2019, March 2019, April 2019, May 2019, June 2019, July 2019, August 2019, September 2019, October 2019, November 2019, December 2019, January 2020, February 2020, April 2020, May 2020,  June 2020 and July 2020, August 2020,  September 2020, October 2020, November 2020 and December 2020, January 2021, February 2021, March 2021, April 2021, May 2021, June 2021 and July 2021.  (And just for fun, go back to, say, July 2017 and see if you can solve the puzzle easily)

Posted in: Volume 16, Issue 8, August 2021, Sports