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[daj95376]

[peterj]

For me this was a real BBDB+ and involved probably one too many glasses of Pouilly Fuisse... My first pass had more finned fish then I can remember, but an intentionally more xy route was this one - for six steps!

[daj95376]

My solver found five necessary steps ... three extraneous steps ... and the lone XY level step was in the middle of the necessary steps.

Peter, nice job of plowing through a rough puzzle!

[Mogulmeister]

Step 1 is an overeach but I stick it out there just to test a new way of text formatting and how not to be beguiled:

1)HUR @ r13c26 and to prevent DP can we really say {356} exists in r134c6 so r8c6 =2 ? ( )

[peterj]

Mm, my undestanding fwiw is that the UR forms a single pseudo-cell of (35) and so to lock the candidates {356} you need two more cells containing only those candidates - not just the one. But I could easily be completely wrong!

[Mogulmeister]

Quite so Peter. I did say it was a lesson on how not to be beguiled. So yes.

It is a good example of a false positive. Something we have all experienced in the 9x9 game.

[Ed]Just looking at that original HUR (without external implications) the only safe elimination that can be made is that the DP will be made if we place 2 into r1c6 so r1c6<>2 but that doesn't advance us very far.

[peterj]

Sorry misunderstood!
One of the problems of using SS rather than paper IMO is you can accidentally (or intentionally ) try those eliminations, find they are hugely constructive and then spend 30 minutes desperately trying to justify them...

[daj95376]

Ouch!!! I missed the necessity of the grouped 2-String Kite. This puzzle was harder than I'd planned. Sorry!!!

[Mogulmeister]

An excellent puzzle Danny - especially if it generates talking points!

[peterj]

It was the lack of "BBDB" label that had me working hard at it - thinking there must be a quicker way.

In some ways it's good not to have the label give too much away - makes it more of a surprise!

[Mogulmeister]

Agreed.

[daj95376]

I (typically) use BBDB on puzzles where my solver seems to need more than four steps. On XY puzzles, I tend not to use BBDB unless there are more than five steps. When I originally counted five steps for this puzzle, I decided to drop the BBDB from the title.

FWIW: I include the BBDB so you won't unexpectedly tackle a puzzle that might be time consuming. This was a problem I heard about previous to using BBDB.

Regards, Danny

[Marty R.]

I used three ERs (5,2,6). After that it was coloring on 2, or something akin to coloring. It might've had an AIC component, but that's not exactly my forte, so I'll leave it at coloring.

P.S. I may have screwed up since I can't re-create my solution using Danny's post-basics grid.

But you tell me if this is valid.

Here's Danny's grid after my three ERs.

[daj95376]

[Marty R.]

Thanks Danny, but I'm all screwed up now. If r7c5=2, then r6c4<>2. If r6c4=2, then r7c5<>2. So with opposite polarity, r6c5<>2. However, maybe that just works out in this case by accident and doesn't have to work out that way as conventional coloring using strong links would.

[daj95376]

[Mogulmeister]

Marty - you have a discontinuous loop with an inherent contradiction (a Baphomet ! )

Just extending on Danny's point a little:

Follow your loop round and you will see that if you start r7c5 as 2 or true when you follow the loop around it becomes false which is a contradiction so r7c5 <>2.

I have colour coded your logic below. Start on the target cell (purple) as true for 2 then follow your sequence. Green is true for 2 and orange is false.

In notation it can be shown as an extension of Danny's chain:

IS 2.........NOT 2......IS 2.........NOT 2.......IS 2
(2)r7c5-r7c9 = r8c8 - r2c8 = r2c4 - r6c4 = r6c5-(2)r7c5 so r7c5<>2

[Marty R.]

Thanks Danny and MM. I'll have to pay more attention to that stuff.

[Mogulmeister]

I've annotated the chain so it might help with the AIC you created.....

If you can look past the guffaws and ribaldry ( ) this thread should help

http://www.dailysudoku.com/sudoku/forums/viewtopic.php?t=4623&highlight=baphomet&sid=25e1d3d76f7ddbfe3299c0d734db2f8b

[daj95376]