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nataraj · Posted: Mon Mar 03, 2008 7:10 am Post subject: Mar 3 - uh hum

Bad start into the week.

How hard is it to solve a puzzle, when after basics (I mean real easy basics) there is just a handful of cell left. When there are mostly those candidate combinations left: 36, 37 and 67 (ok, there is also 69 and three tri-values)

I am sure there are a lot of fancy ways to take the last step. That does not take my frustration away, right now. Sad

Earl · Joined: 30 May 2007 Posts: 677 Location: Victoria, KS

I agree. Just an xy-wing pivoted at R8C2.

Earl

Marty R. · Posted: Mon Mar 03, 2008 4:43 pm Post subject:

One W-Wing on the 37s was all that was needed.

KSipher · Joined: 24 Sep 2006 Posts: 38

Hi
Can someone point me to a link that explains w-wings! Thanks.
Kathy

Marty R. · Posted: Mon Mar 03, 2008 5:50 pm Post subject:

Kathy, a W-wing occurs when there are two cells with the same pair and they are connected by a strong link on one of the numbers. Then the other numbers become pincers, working like the pincers of an XY-Wing.

The fourth post here gives an example. If it's not enough information, just ask for more detail and someone will be happy to answer.

http://www.dailysudoku.co.uk/sudoku/forums/viewtopic.php?t=2143

storm_norm · Joined: 18 Oct 2007 Posts: 1741

xy-wing for me

KSipher · Joined: 24 Sep 2006 Posts: 38

Marty

I understood the link you mentioned and could follow the w-wing as described. I don't know if I ever will be able to spot one. In particular, I cannot see the w-wing based on 37. Can you point it out to me.
Thanks

Kathy

Marty R. · Posted: Tue Mar 04, 2008 12:33 am Post subject:

KSipher · Joined: 24 Sep 2006 Posts: 38

Marty

Here is my grid at the point where I started looking for the elusive w-wing.

Kathy

Stanley P · Joined: 27 Feb 2008 Posts: 20 Location: Tennessee, USA

I am pretty new to this forum. I saw the xy-wing for rows 1,8,9 and cols 2,3 which eliminated the 3 in r2c2. With a previous x-wing I think, that did it for me. Like KSipher I missed the w-wing and would like to know where it occurs.

Marty R. · Posted: Tue Mar 04, 2008 4:52 am Post subject:

nataraj · Posted: Tue Mar 04, 2008 6:47 am Post subject:

Some more things to see in the grid posted by KSipher:

The xy-wings in boxes 1 and 7 can be seen either as 37-36-67 pivoted on r8c2 (as Earl remarked) which takes out the 7 in r1c3, or as 36-67-37 pivoted on r9c3, in which case it takes out the 3 in r2c2 (Stanley's).

Furthermore, in box 8, "7" is restricted to col r79c5, thus 7 can be removed from cell r1c5.
We now have another xy-wing 36-37-67 pivoted on r1c3 which takes out 6 in r9c5.

The 36 and 37 cells form a ring

KSipher · Joined: 24 Sep 2006 Posts: 38

Thanks for the comments. Marty, I finally can see the w-wing - I finally got it. I even think I can recognize it in the future, with a little practice.

Now I need to spend a little time trying to digest all the comments nataraj made. It's been a busy day, so tomorrow I will work on following it.

I love this group - so many generous offers of help!

Kathy

ravel · Joined: 21 Apr 2006 Posts: 536

nataraj · Posted: Thu Mar 06, 2008 12:24 pm Post subject:

To complete the zoo of wings, there is also an x-wing (on 3, in cols 3 and 5) which turns the situation into a BUG+1, easily recognized by having only one cell with more than 2 candidates:

Asellus · Posted: Fri Mar 07, 2008 4:00 am Post subject:

I was wondering if anyone was going to find the X-Wing and BUG+1. That's how I happened to solve it.