## Stuck on Expert puzzle from Fingerarts Sudoku version 6.7

Post the puzzle or solving technique that's causing you trouble and someone will help

### Stuck on Expert puzzle from Fingerarts Sudoku version 6.7

Hi Forum.
I have recently moved from the Hard to Expert level puzzles in my Sudoku app.
For the life of me, I cannot crack this one.
https://imgur.com/Rch7I3K

I have exhausted the basic solving techniques (including X-Wing and Swordfish).
What am I missing?

Best regards.
Tordenskjold

Posts: 2
Joined: 12 September 2018

### Re: Stuck on Expert puzzle from Fingerarts Sudoku version 6.

Hello. First, you haven't actually exhausted all basics. There's a naked pair (48) / hidden pair (69) on row 2, as well as a hidden pair (69) / naked quad (2458) on column 4. They don't really make a difference, though.

This puzzle requires at least one relatively advanced technique (AIC or Sue de Coq, for example) to solve. There are a couple of simpler Unique Rectangles and a W-Wing available, but they're not enough to solve the puzzle. The simplest single move that leaves just singles is probably this short AIC (or one of its variants):

Code: Select all
`.-----------------.------------------.--------------.| 6    3      9   | 458   2     458  | 7     1   48 || 5    7      1   | 4689  4689  48   | 3     2   48 || 8    2      4   | 7     3     1    | 9     6   5  |:-----------------+------------------+--------------:| 1   d(8)-4  6   | 2458  4578  9    |a2(4)  57  3  || 47   9     c278 | 3     4578  6    |b24    57  1  || 347  5      237 | 24    1     247  | 6     8   9  |:-----------------+------------------+--------------:| 347  468    378 | 1     678   378  | 5     9   2  || 2    68     358 | 5689  5689  358  | 1     4   7  || 9    1      57  | 245   457   2457 | 8     3   6  |'-----------------'------------------'--------------'`

(4=2)r4c7 - r5c7 = (2-8)r5c3 = (8)r4c2 => -4 r4c2; stte

The chain proves that either r4c7=4 or r4c2=8; in both cases r4c2<>4. Once you eliminate that, the rest is easy.

PS. If I'm not wrong, some people call that chain pattern an H2-Wing. But I may very well be wrong, so I'd appreciate if someone either confirmed or corrected that. (Not that it really matters what it's called as long as it works.)
-SpAce-: Show
Code: Select all
`   *             |    |               |    |    *        *        |=()=|    /  _  \    |=()=|               *            *    |    |   |-=( )=-|   |    |      *     *                     \  ¯  /                   *    `

"If one is to understand the great mystery, one must study all its aspects, not just the dogmatic narrow view of the Jedi."

SpAce

Posts: 2579
Joined: 22 May 2017

### Re: Stuck on Expert puzzle from Fingerarts Sudoku version 6.

Thank you so much.
That was very educational.

I guess that is the wondrous world of Sudoku. Always nuances to learn.