## Help with tricky sudoku

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

### Help with tricky sudoku

Hello!

I started out with the following grid:

***6**4**
7****36**
****91*8*
*********
*5*18***3
***3*6*45
*4*2***6*
9*3******
*2****1**

I have now reached the following candidates:

{12358}{1389}{12589}{6}{257}{2578}{4}{23579}{1279}
{7}{189}{124589}{458}{245}{3}{6}{259}{129}
{23456}{36}{2456}{457}{9}{1}{2357}{8}{27}
{2348}{3789}{2489}{4579}{2457}{2457}{2789}{1}{6}
{246}{5}{2469}{1}{8}{2479}{279}{279}{3}
{128}{1789}{1289}{3}{27}{6}{2789}{4}{5}
{158}{4}{1578}{2}{13}{5789}{3579}{6}{789}
{9}{16}{3}{4578}{16}{4578}{257}{257}{2478}
{568}{2}{5678}{45789}{36}{45789}{1}{3579}{4789}

Now I am completely lost, I don’t see any more possible eliminations. Can you please help me?

/Anette
Anette

Posts: 55
Joined: 09 June 2005

I don't think it's possible with any of the non-trial&error tactics that one could resonably be expected to perform in a newspaper. I'm sure it can be done with colouring or some such thing, but I don' really know about that stuff.
PaulIQ164

Posts: 533
Joined: 16 July 2005

Where is this puzzle from?

At the end of simple logic, there were five 2-candidate cells that connect and no way of making a forcing chain using them alone.

However, I can make a short chain of "True/false" or "conjugate" type links through cells with more than 2 candidates that will combine with the 2-candidate cells to form a forcing chain:

r3c2=3 => r3c7<>3 => r7c7=3 => r7c5=1 => r8c5=6
r3c2=6 => r8c2=1 => r8c5=6
Therefore r8c5=6

The rest solves easily.

Here's the simplified diagram. The two 3s in () are the only two cells in column 7 that can contain a 3. This is the "true/false" or "conjugate" link in the chain.

Code: Select all
`  .   .   .  |  .   .   .  |  .   .   .    .   .   .  |  .   .   .  |  .   .   .    .  36   .  |  .   .   .  | (3)  .   .    -----------+-------------+-----------   .   .   .  |  .   .   .  |  .   .   .    .   .   .  |  .   .   .  |  .   .   .    .   .   .  |  .  13   .  | (3)  .   .    -----------+-------------+-----------   .   .   .  |  .   .   .  |  .   .   .    .  16   .  |  .  16   .  |  .   .   .    .   .   .  |  .   .   .  |  .   .   . `
tso

Posts: 798
Joined: 22 June 2005

It's from a Norwegian sudokusite and was labelled "very difficult" ("super vanskelig". http://www.menneske.no/sudoku/

Since all Swedish "very difficult"'s I've found have been rather simple, I didn't expect this one to be too tough either. But apparently Norway has come further than Sweden (I hope no Norwegians see this, there is constant teasing between our countries regarding the mental capacity).
Anette

Posts: 55
Joined: 09 June 2005

Now I see a reference to this site in another thread, which says ""Super Vanskelig" can sometimes only be solved by Trevor's Tables."

I have no clue what Trevor's Tables are, and since it is Friday evening I don't even want to know right now..........
Anette

Posts: 55
Joined: 09 June 2005

This link discusses trebor's tables, but it looks like heavy going.

http://www.setbb.com/phpbb/viewtopic.php?t=126&highlight=tables&mforum=sudoku

S
simes

Posts: 324
Joined: 11 March 2005
Location: UK