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JUL 2 VH

 
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roaa



Joined: 18 Apr 2009
Posts: 80
Location: Sweden

PostPosted: Wed Jul 02, 2014 8:03 am    Post subject: JUL 2 VH Reply with quote

The usual! The XY-wing 467 forces r7c5 and r9c5 <>7 which is enough.
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hughwill



Joined: 05 Apr 2010
Posts: 227
Location: Birmingham UK

PostPosted: Wed Jul 02, 2014 8:36 am    Post subject: Jul 2 VH Reply with quote

After basics:

Code:

+--------+------------+-------------+
| 6 8  5 | 2   47  9  | 134 347 137 |
| 3 9  4 | 567 167 15 | 2   67  8   |
| 2 7  1 | 46  8   3  | 46  5   9   |
+--------+------------+-------------+
| 8 5  3 | 1   2   4  | 7   9   6   |
| 4 1  7 | 3   9   6  | 58  28  25  |
| 9 2  6 | 8   5   7  | 134 34  13  |
+--------+------------+-------------+
| 5 4  8 | 67  367 2  | 9   1   37  |
| 7 36 9 | 45  14  15 | 368 368 2   |
| 1 36 2 | 9   37  8  | 5   367 4   |
+--------+------------+-------------+

Play this puzzle online at the Daily Sudoku site


Same answer jumped out. Didn't even need to look for the 67 W-Wing
in c5 setting r2c4 to 5!

Hugh
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Marty R.



Joined: 12 Feb 2006
Posts: 5178
Location: Rochester, NY, USA

PostPosted: Wed Jul 02, 2014 2:53 pm    Post subject: Re: Jul 2 VH Reply with quote

hughwill wrote:
After basics:

Code:

+--------+------------+-------------+
| 6 8  5 | 2   47  9  | 134 347 137 |
| 3 9  4 | 567 167 15 | 2   67  8   |
| 2 7  1 | 46  8   3  | 46  5   9   |
+--------+------------+-------------+
| 8 5  3 | 1   2   4  | 7   9   6   |
| 4 1  7 | 3   9   6  | 58  28  25  |
| 9 2  6 | 8   5   7  | 134 34  13  |
+--------+------------+-------------+
| 5 4  8 | 67  367 2  | 9   1   37  |
| 7 36 9 | 45  14  15 | 368 368 2   |
| 1 36 2 | 9   37  8  | 5   367 4   |
+--------+------------+-------------+

Play this puzzle online at the Daily Sudoku site


Same answer jumped out. Didn't even need to look for the 67 W-Wing
in c5 setting r2c4 to 5!

Hugh


Hugh,

I don't understand how the wing sets r2c4 to 5. The wing does some damage, but I don't see that conclusion. Question
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hughwill



Joined: 05 Apr 2010
Posts: 227
Location: Birmingham UK

PostPosted: Wed Jul 02, 2014 5:56 pm    Post subject: Reply with quote

Hi Marty

I may be wrong here but:

If r2c8 = 6 then r2c5<>6, r7c5 must be 6 making r7c4=7
If r7c4=6 then r7c5<>6 and r2c5 must be 6 making r2c8=7

Either way the 67s act as a pair, so r2c4<>7 or 6 and so =5

Have I made an error?

Hugh
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keith



Joined: 19 Sep 2005
Posts: 3184
Location: near Detroit, Michigan, USA

PostPosted: Wed Jul 02, 2014 8:07 pm    Post subject: Reply with quote

Hugh,

Your grid has unsolved basics in R5B6 and R8C8. And yes, the 67s are a remote pair, seen as a pair of w-wings with a link on 6 in R3 and a link on 7 in C9.

Keith
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Marty R.



Joined: 12 Feb 2006
Posts: 5178
Location: Rochester, NY, USA

PostPosted: Wed Jul 02, 2014 8:37 pm    Post subject: Reply with quote

hughwill wrote:
Hi Marty

I may be wrong here but:

If r2c8 = 6 then r2c5<>6, r7c5 must be 6 making r7c4=7
If r7c4=6 then r7c5<>6 and r2c5 must be 6 making r2c8=7

Either way the 67s act as a pair, so r2c4<>7 or 6 and so =5

Have I made an error?

Hugh


I don't know if you've made an error or not because a glaring weakness of mine is the inability to follow along with that style of reasoning. However, your premise of either r2c8 or r7c4 being 6 puzzles me because I don't see anything that says either of those two cells must be 6. Perhaps someone else will come along and straighten me out.

But my original response was about the statement about the W-Wing, "Didn't even need to look for the 67 W-Wing
in c5 setting r2c4 to 5!"

The W-Wing consists of 67 cells in r2c8 and r7c4, connected by the strong link on 6 in c5. That says at least one of r2c8 and r7c4 must be 7, thus making r2c4<>7.
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keith



Joined: 19 Sep 2005
Posts: 3184
Location: near Detroit, Michigan, USA

PostPosted: Wed Jul 02, 2014 9:18 pm    Post subject: Reply with quote

Quote:
connected by the strong link on 6 in c5
Question Question
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Lee



Joined: 10 Jun 2014
Posts: 17
Location: San Francisco

PostPosted: Wed Jul 02, 2014 10:25 pm    Post subject: Reply with quote

Hello Everyone,

Have to get in my two cents.

Looks to me like r2c4 is connected by two w-wings both using the same end points (r7c4 and r2c8):

The first w-wing involves a strong link on 6 in c5 as pointed out by Marty.

The second w-wing involves a strong link on 7 in block 9 (r7c9 to r9c8).

The first w-wing eliminates the 7 from r2c4. The second w-wing eliminates the 6 from r2c4. Thus between the two we are left with a 5 in r2c4.

This seems pretty strange, but it also seems to be true, or am I really confused?

Comments???
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Marty R.



Joined: 12 Feb 2006
Posts: 5178
Location: Rochester, NY, USA

PostPosted: Wed Jul 02, 2014 11:23 pm    Post subject: Reply with quote

keith wrote:
Quote:
connected by the strong link on 6 in c5
Question Question


Keith,

What's the question? I may have missed the fact that there was a double W-Wing, but each 6 in c5 sees a 67 cell based on the posted grid.
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keith



Joined: 19 Sep 2005
Posts: 3184
Location: near Detroit, Michigan, USA

PostPosted: Wed Jul 02, 2014 11:26 pm    Post subject: Reply with quote

Marty R. wrote:
keith wrote:
Quote:
connected by the strong link on 6 in c5
Question Question


Keith,

What's the question? I may have missed the fact that there was a double W-Wing, but each 6 in c5 sees a 67 cell based on the posted grid.


Marty,

Thank you, I would not have recognized it as a strong link.

Keith
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Marty R.



Joined: 12 Feb 2006
Posts: 5178
Location: Rochester, NY, USA

PostPosted: Wed Jul 02, 2014 11:30 pm    Post subject: Reply with quote

Quote:
This seems pretty strange, but it also seems to be true, or am I really confused?


Sounds good to me. What really seems strange is that there are two strong links on both 6 and 7.
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keith



Joined: 19 Sep 2005
Posts: 3184
Location: near Detroit, Michigan, USA

PostPosted: Thu Jul 03, 2014 1:33 am    Post subject: Reply with quote

Marty R. wrote:
Quote:
This seems pretty strange, but it also seems to be true, or am I really confused?


Sounds good to me. What really seems strange is that there are two strong links on both 6 and 7.

Marty,

The double W-wing is not that rare. What's more, it always makes a cycle, in which all links become strong.
Code:
+-------------+-------------+-------------+
| 6   8   5   | 2   47  9   |134 34-7 e137|
| 3   9   4   |5-67 167 15  | 2  d67  8   |
| 2   7   1   |b46  8   3   |c46  5   9   |
+-------------+-------------+-------------+
| 8   5   3   | 1   2   4   | 7   9   6   |
| 4   1   7   | 3   9   6   | 8   2   5   |
| 9   2   6   | 8   5   7   | 134 34  13  |
+-------------+-------------+-------------+
| 5   4   8   |a67 36-7 2   | 9   1  f37  |
| 7   36  9   | 45  14  15  | 36  8   2   |
| 1   36  2   | 9   37  8   | 5   367 4   |
+-------------+-------------+-------------+

In this case a6b6c6d7e7f7a, in my pidgin notation

In other words, buddies of a and b cannot be 6, of f and a cannot be 7, etc. I have marked the eliminations I can see.

Some M-wings are also often cycles.

Here is another XY cycle in the same grid, found by Sudoku Susser:
Code:
Found a 7-link Simple Forcing Loop.  If we assume that square [x=2,y=9] is <3> then we can make the following chain of conclusions:

   [x=5,y=9] must be <7>, which means that
   [x=4,y=7] must be <6>, which means that
   [x=4,y=3] must be <4>, which means that
   [x=7,y=3] must be <6>, which means that
   [x=7,y=8] must be <3>, which means that
   [x=2,y=8] must be <6>, which means that
   [x=2,y=9] must be <3>.

This forms a inherently bi-directional loop through the puzzle that permits reductions.  On each edge of the loop, one of the two squares must have a particular value, so their common buddies cannot contain that value, as follows:

   One of [x=2,y=9] and [x=5,y=9] must be <3>.
   One of [x=5,y=9] and [x=4,y=7] must be <7>.
   One of [x=4,y=7] and [x=4,y=3] must be <6>.
   One of [x=4,y=3] and [x=7,y=3] must be <4>.
   One of [x=7,y=3] and [x=7,y=8] must be <6>.
   One of [x=7,y=8] and [x=2,y=8] must be <3>.
   One of [x=2,y=8] and [x=2,y=9] must be <6>.

Thus we can deduce that:

   [x=8,y=9] - cannot contain <3> because of [x=2,y=9] and [x=5,y=9].
   [x=5,y=7] - cannot contain <7> because of [x=5,y=9] and [x=4,y=7].
   [x=4,y=2] - cannot contain <6> because of [x=4,y=7] and [x=4,y=3].


Keith
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hughwill



Joined: 05 Apr 2010
Posts: 227
Location: Birmingham UK

PostPosted: Thu Jul 03, 2014 7:10 pm    Post subject: Reply with quote

Marty wrote:

Quote:
I don't know if you've made an error or not because a glaring
weakness of mine is the inability to follow along with that style of reasoning.
However, your premise of either r2c8 or r7c4 being 6 puzzles me because I
don't see anything that says either of those two cells must be 6. Perhaps
someone else will come along and straighten me out.


Yes Marty- you've seen the flaw in my logic- of course (without the
strong link in C9 on 7 from later contributors) there is no reason
why one of these squares must be 6. I might have got the right
answer, but through wrong reasoning!

Hugh
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keith



Joined: 19 Sep 2005
Posts: 3184
Location: near Detroit, Michigan, USA

PostPosted: Fri Jul 04, 2014 1:33 pm    Post subject: Reply with quote

Note the M-wing that solves it in one step:
Code:
+-------------+-------------+-------------+
| 6   8   5   | 2   47  9   | 134 347 137 |
| 3   9   4   |B567 1-67 15 | 2  A67  8   |
| 2   7   1   | 46  8   3   | 46  5   9   |
+-------------+-------------+-------------+
| 8   5   3   | 1   2   4   | 7   9   6   |
| 4   1   7   | 3   9   6   | 8   2   5   |
| 9   2   6   | 8   5   7   | 134 34  13  |
+-------------+-------------+-------------+
| 5   4   8   |C67 D367 2   | 9   1   37  |
| 7   36  9   | 45  14  15  | 36  8   2   |
| 1   36  2   | 9   37  8   | 5   367 4   |
+-------------+-------------+-------------+
The logic is:
If A is 7, B is not 7, C is 7. If C is not 6, D is 6. AD are pincers on 6, taking 6 from R2C5 and solving the puzzle..

Keith
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Marty R.



Joined: 12 Feb 2006
Posts: 5178
Location: Rochester, NY, USA

PostPosted: Fri Jul 04, 2014 3:11 pm    Post subject: Reply with quote

Now that's something that I do see frequently--Remote Pairs being able to be played as both M- and W-Wings.
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