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Well, this sure looks intimidating, right? Let’s see if we can find the inherent weakness in this puzzle, the hidden clue that once revealed, will break down the barriers!
Steps 1-5 reveal no clues! It looks like we may be in some kind of trouble here. Let’s see if Step 6 can help us.
There are 3 circumstances that establish the potential for a Step 6 exercise: - 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**. - Look for
**just 2 unsolved****cells**in a**column**that contain the**same option**where these 2 cells are**not in the same box**. - 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 row 3, we find just 2 unsolved cells that contain #1 as an option … C1R3 & C7R3. These cells are not in the same box, thereby qualifying as a candidate for a Step 6 exercise. These cells are highlighted below in Example #33.2 below:
One of these two yellow cells must be a 1. We will consider them as “ Here is the We will mark C1R3 with a “Y” and mark C7R3 with a lower case “y” to keep track of the exercise as per Example #33.3 below. If C1R3=1 (marked with a Y), then C1R7 cannot be a 1 and we mark it below with a “N” for no. If C7R3=1(marked as a y), then C7R5 & C7R6 are not a 1 and we mark them with a n. The only other cell in box 6 that can be a 1 is C8R6. Mark it with a y. Then C5R6=n and C6R6=n. Then C6R5=y. Then C6R7=n and C6R9=n. Then C5R7=y, and C1R7=n. Now look at C1R7 with its “N,n” designation. It is not a 1 regardless of which yellow cell is a 1. Therefore, you can remove a 1 as an option from C1R7.
Now your grid should look like Example #33.4 below:
Having deleted the 1 in C1R7 gives us just 2 cells in box 7 that can be a 1, C2R7 & C2R9; therefore, just one of these cells in column 2 must be a 1. This sets up a Step 2 Interaction, eliminating the 1 as an option in C2R2. Since there are no more Step 1-5 clues, we will look for another Step 6 potential. In Example #33.5 below we have highlighted 2 more cells that are a potential Step 6 exercise.
The 2 yellow highlighted cells are the only 2 cells in row 3 that have a 9 as an option, and they are not in the same box, thus qualifying for a Step 6 exercise. We will first assume C1R3 is a 9 and mark it with a Y as per above example. Next, we will assume C9R3 is a 9 and mark it with a y. Track each of the 2 yellow cells with the yes’s and no’s and you have the result of a “N,n” designation in C1R8. So C1R8 is not a 9 regardless of which yellow cell is a 9, eliminating the 9 as an option from C1R8. This gives you Example #33.6 below:
So, has this Step 6 been more productive? Let’s look at column 1. C1R3 is now the only cell in column 1 that can be a 9. C1R3=9. Then C9R3=7, C4R3=5, and you are off to the races in solving this puzzle. Now your completed grid should look like Example #33.7 below:
Hope you enjoyed this puzzle. It is yet another example of how a Step 6 exercise exposed the weakness in a puzzle that looked so difficult. See you on February 15, 2018. May the gentle winds of Sudoku be at your back.
By Dan LeKander, Wellesley Island
[See Jessy Kahn’s Book Review, “3 Advanced Sudoku Techniques…” by Dan LeKander, June issue of TI Life.]
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