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garytorborg · Joined: 19 Jan 2011 Posts: 28

I'm stuck in a fiendish puzzle on an android version of the game. I've solved other fiendish puzzles before without help but this one has got me stumped, and the only thing I can think of is that I am missing a candidate somewhere. The software will not give me hints (I don't want any anyway) and it tells me that I am "correct so far".

After basics, an xy-wing, an xyz-wing, and looking at the 2 w-wings (neither of which result in any eliminations), I am at this point:

peterj · Joined: 26 Mar 2010 Posts: 974 Location: London, UK

As far as I can see you have "solved" it Question

The grid you posted has a solved 1 in block 9 but still a candidate in r7c8?
If you look at 7's in block 9 you should see a next move also...

garytorborg · Joined: 19 Jan 2011 Posts: 28

Oops! The cell in question was mis-typed by me, and I didn't proof-read properly. The candidates in r7c8 should be: 379. Here's the corrected code:

keith · Posted: Thu Jan 20, 2011 12:16 am Post subject:

Next, an X-wing on 9 in R19.

Keith

daj95376 · Joined: 23 Aug 2008 Posts: 3854

After the X-Wing, I don't see anything "pleasant".

peterj · Joined: 26 Mar 2010 Posts: 974 Location: London, UK

I am not sure this counts as "pleasant"! "Effective" perhaps is the word...

(Before the x-wing...)

garytorborg · Joined: 19 Jan 2011 Posts: 28

peterj · Joined: 26 Mar 2010 Posts: 974 Location: London, UK

OK - you asked for it!

So an "almost" pattern is a way of tackling harder puzzles but still basing it on searching for named patterns. The idea is to find something that would be a pattern e.g. a wing or fish, if it weren't for one (or more) candidates that get in the way.

Notation means..

One of the following statements must be true...
1) there is an xy-wing(69-5) pivoted on r7c6
2) there is a 3 in r7c6

(1) leads to r8c6<>5 as usual for an xy-wing
(2) results in a chain as follows:
if (3)r7c6 then (8)r7c9 and so (9)r8c7...
so not (9)r7c8 and must be a 9 in r7c5 or r7c6..
so as 9 in block 8 r9c5 must be a 5 - hence r8c6 can't be 5

Since both possibilities result in the same elimination we can remove 5 from r8c6. We don't know which initial proposition is true (in fact the xy-wing is true) but in either case the same elimination can be made.

garytorborg · Joined: 19 Jan 2011 Posts: 28

Thank you, PeterJ!

I have never before used an "almost" pattern, as you describe there, but it worked perfectly. After the elimination, a quad appeared in row 8, eliminating no less than 2 more 9s, and then it came tumbling down.

keith · Posted: Fri Jan 21, 2011 5:27 pm Post subject: