dailysudoku.com Forum Index dailysudoku.com
Discussion of Daily Sudoku puzzles
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

Dec 15 vh
Goto page Previous  1, 2
 
Post new topic   Reply to topic    dailysudoku.com Forum Index -> Daily Sudoku puzzles
View previous topic :: View next topic  
Author Message
nataraj



Joined: 03 Aug 2007
Posts: 1047
Location: near Vienna, Austria

PostPosted: Sun Dec 16, 2007 6:27 pm    Post subject: Reply with quote

Marty R. wrote:
It's fun to do pincer coloring since it's relatively new to me. Wink


Same here. I really like this approach (and it's fairly new to me as well). Smile

I guess I like it because it offers a small amount of order in chaos - those xy-chains are a pain to look for and with those xy-wings (even when "useless" at first glance) one at least has a starting point.
Back to top
View user's profile Send private message Send e-mail Visit poster's website
cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Sun Dec 16, 2007 9:34 pm    Post subject: Reply with quote

[quote]XZ-XY-YZ=YZ=YZ[quote]

The xy-wing I used was the <58> pivot and <35> <38> pincers shown below. I see the XZ-XY-YZ=YZ=YZ sequence here - but isn't the =YZ bit (removing the <3> in R7) just the expected outcome of the wing technique. And once this <3> is removed, there's simply a naked <8> in Box 3.
I guess what I'm saying is: does the "=YZ=YZ" need a special name (pincer colouring) -when it's really just back to basics - or as we used to say in the UK - "it all comes out in the wash".

Code:
            
+-------+-------+-------+   
| . .  .| . . . | . 38. |   
| . .  .| . . . | . . . |   
| . 35 .| . . . | . . . |   
+-------+-------+-------+   
| . . . | . . . | . . . |   
| . . . | . . . | . . . |   
| . . . | . . . | . . . |   
+-------+-------+-------+   
| . .  .| . . . | . 38. |   
| . .  .| . . . | . . . |   
| . 58 .| . . . |38 . . |
+-------+-------+-------+
Back to top
View user's profile Send private message
keith



Joined: 19 Sep 2005
Posts: 3329
Location: near Detroit, Michigan, USA

PostPosted: Sun Dec 16, 2007 10:05 pm    Post subject: Reply with quote

[quote="cgordon"][quote]XZ-XY-YZ=YZ=YZ
Quote:


The xy-wing I used was the <58> pivot and <35> <38> pincers shown below. I see the XZ-XY-YZ=YZ=YZ sequence here - but isn't the =YZ bit (removing the <3> in R7) just the expected outcome of the wing technique. And once this <3> is removed, there's simply a naked <8> in Box 3.
I guess what I'm saying is: does the "=YZ=YZ" need a special name (pincer colouring) -when it's really just back to basics - or as we used to say in the UK - "it all comes out in the wash".

Code:
            
+-------+-------+-------+   
| . .  .| . . . | . 38. |   
| . .  .| . . . | . . . |   
| . 35 .| . . . | . . . |   
+-------+-------+-------+   
| . . . | . . . | . . . |   
| . . . | . . . | . . . |   
| . . . | . . . | . . . |   
+-------+-------+-------+   
| . .  .| . . . | . 38. |   
| . .  .| . . . | . . . |   
| . 58 .| . . . |38 . . |
+-------+-------+-------+


You need to read the second post in the thread. Carefully. The XY-wing you cite does solve the puzzle directly. But, the extended XY-wing is different. It is:
Code:
            
+-------+-------+-------+   
| . . 35| . . . | . 38. |   
| . .  .| . . . | . . . |   
| . 35 .| . . . | . . . |   
+-------+-------+-------+   
| . . . | . . . | . . . |   
| . . . | . . . | . . . |   
| . . . | . . . | . . . |   
+-------+-------+-------+   
| . .  .| . . . | . 38. |   
| . .  .| . . . | . . . |   
| . 58 .| . . . |38 . . |
+-------+-------+-------+

It has <38> as a pivot, <35> and <58> as pincers, and takes out <5> in R3C2.

Warning: "Sophisticate" status in jeopardy! Wink Razz
Back to top
View user's profile Send private message
cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Sun Dec 16, 2007 11:00 pm    Post subject: Reply with quote

Keith:
Yeah yeah - now I see it. You are sticking the "=YZ=YZ" bit in the middle of the "XZ-XY-YZ" bit - not at the end. What troubles me is that two prominent regulars agreed that this method was fun.
Sophisticates are not usually into hard work and unnecessary labouring.
Back to top
View user's profile Send private message
nataraj



Joined: 03 Aug 2007
Posts: 1047
Location: near Vienna, Austria

PostPosted: Mon Dec 17, 2007 11:03 pm    Post subject: Reply with quote

Craig,

rest assured, I am not "into hard work and unnecessary labouring" (but then again I would not call myself a sophisticate ... Laughing )

On the contrary, I am quite lazy. So when I've gone to all that trouble and finally found an xy-wing, I try and check all other possibilities, even when at first glance the xy-wing doesn't eliminate anything.

It is like a salvage operation. Or, you could say, it is two shots for the price of one. Amazingly often, the extension of such a wing, be it at either end or in the middle, yields a useful result. In my experience, it is MUCH easier to spot xy-wings that way.

Long live the flightless bird!

Back to top
View user's profile Send private message Send e-mail Visit poster's website
keith



Joined: 19 Sep 2005
Posts: 3329
Location: near Detroit, Michigan, USA

PostPosted: Mon Dec 17, 2007 11:39 pm    Post subject: Reply with quote

Nataraj,

Great picture!

(All: The inside joke here is that some of us are naming these "useless" wings that make no direct eliminations as "flightless" wings.)

Nataraj is correct: If you are looking for XY-wings and find one that does not make an elimination, look to see if you can extend it by coloring.

Or, if you have a chain XY=XY=XY, see if it can be the pivot of an extended XY-wing.

Last night I was looking at the discussions from a year or two ago. It is incredible how the human-recognizable pencil and paper techniques have evolved and improved.

Keith
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    dailysudoku.com Forum Index -> Daily Sudoku puzzles All times are GMT
Goto page Previous  1, 2
Page 2 of 2

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group