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May 1 VH

 
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Earl



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

PostPosted: Fri May 01, 2009 2:14 am    Post subject: May 1 VH Reply with quote

Truly VH. A three-stepper for me. Any single shots out there?

A Solution: X-wing <4>, xy-wing (168), xy-chain eliminates 7 in R8C8. The <38> UR seems ineffective

Early Earl
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA

PostPosted: Fri May 01, 2009 4:39 am    Post subject: Reply with quote

Do I hang my head in shame if I used five steps?

Quote:
X-Wing (4), Hidden UR (38), and three XY-Wings (681, 147, 487)
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA

PostPosted: Fri May 01, 2009 6:26 am    Post subject: Reply with quote

Not using the UR, I had:

Quote:
X 4, XY with transport 46-8, XYZ -147, extended XY 78 48 46 67


Keith
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA

PostPosted: Fri May 01, 2009 6:33 am    Post subject: Reply with quote

At last, a "very hard" worthy of the name. I think the minimal path is an XYZ-wing followed by an XY-wing.

After basics:
Code:
+-------------------+-------------------+-------------------+
| 5     168   14    | 7     3     148   | 2     9     16    |
| 9     178   147   | 2     6     5     | 48    3     17    |
| 38    13678 2     | 48    9     148   | 468   47    5     |
+-------------------+-------------------+-------------------+
| 38    38    5     | 6     2     9     | 7     1     4     |
| 7     19    19    | 5     48    48    | 3     6     2     |
| 4     2     6     | 3     1     7     | 9     5     8     |
+-------------------+-------------------+-------------------+
| 6     79    79    | 48    5     2     | 1     48    3     |
| 2     4     3     | 1     78    6     | 5     78    9     |
| 1     5     8     | 9     47    3     | 46    2     67    |
+-------------------+-------------------+-------------------+


Keith
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nataraj



Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria

PostPosted: Fri May 01, 2009 7:22 am    Post subject: Reply with quote

great puzzle. truly very hard

I could not believe I needed all of these steps (I did not use the 38 UR):

- x wing (4)
- xy-wing 18-68-16
- xyz 14-147-17
- xy 47-48-87
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Fri May 01, 2009 8:01 am    Post subject: Reply with quote

Earl wrote:
Quote:
Any single shots out there?

Earl, you had to ask.
notice that if the 8 in C is false then the naked triple {179} in column 2 is true in ABC
also if the naked triple is true then the 7 in F is false.
a chain can be formed.
Code:
.---------------------.---------------------.---------------------.
| 5      168    14    | 7      3      148   | 2      9      16    |
| 9     C178    147   | 2      6      5     |D48     3      17    |
| 38   F136-78  2     | 48     9      148   |E468    47     5     |
:---------------------+---------------------+---------------------:
| 38     38     5     | 6      2      9     | 7      1      4     |
| 7     B19     19    | 5      48     48    | 3      6      2     |
| 4      2      6     | 3      1      7     | 9      5      8     |
:---------------------+---------------------+---------------------:
| 6     A79     79    | 48     5      2     | 1      48     3     |
| 2      4      3     | 1      78     6     | 5      78     9     |
| 1      5      8     | 9      47     3     | 46     2      67    |
'---------------------'---------------------'---------------------'

nt = naked triple
(nt179)ABC = (8)C - (8)D = (8-6)E = (6)F; F is not 7

the chain says that either the naked triple is true, in which case the 7 can't exist in F
or
the 6 is true in F... which also means 7 can't exist in F
either way, the removal of that 7 provides a single step solution.
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Ema Nymton



Joined: 17 Apr 2009
Posts: 89

PostPosted: Fri May 01, 2009 11:04 am    Post subject: Reply with quote

.
Please I ask your indulgences. Like a school child, I follow my teacher's instruction without questioning because I believe that eventually understanding will come through use of the formula. (Sounding a bit 'Moody Blues'ish) ;-/


keith wrote:
At last, a "very hard" worthy of the name. I think the minimal path is an XYZ-wing followed by an XY-wing.

After basics:
Code:
+-------------------+-------------------+-------------------+
| 5     168   14    | 7     3     148   | 2     9     16    |
| 9     178   147   | 2     6     5     | $48   3     17    |
| 38    13678 2     | #48   9     148   | 468  #47    5     |
+-------------------+-------------------+-------------------+
| 38    38    5     | 6     2     9     | 7     1     4     |
| 7     19    19    | 5     48    48    | 3     6     2     |
| 4     2     6     | 3     1     7     | 9     5     8     |
+-------------------+-------------------+-------------------+
| 6     79    79    | 48    5     2     | 1     48    3     |
| 2     4     3     | 1     78    6     | 5     #78   9     |
| 1     5     8     | 9     47    3     | 46    2     67    |
+-------------------+-------------------+-------------------+


Keith


Following the 'XY Wing' rule that because '8' cannot exist outside of the '# buddies', the the money square is 4/8 at r2,c7.
(Accepting this as gospel, I'd like to understand the 'why' of it.)

A willing student....

~@:o?
.
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nataraj



Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria

PostPosted: Fri May 01, 2009 12:13 pm    Post subject: Reply with quote

Ema,

you got to be careful with "rules".

The "XY-rule" does not say anything about "outside the # buddies".
The xy-wing you found (like any other xy- or w- or m-wing) only allows a deduction about those cells that see both ends ("pincers") of the wing: they cannot contain the candidate that is present in both pincers.

In this case, the pincers are r3c4 and r8c8, the common candidate is "8", and the only cell that sees both pincers is r8c4. The xy-wing asserts that r8c4 cannot be 8. Which is kind of trivial because we already know it is "1".

A wing like this is called "useless" or "flightless" in this forum. It might lead to other eliminations (by way of "transporting" or "coloring") but in itself does not help the solution.

The cell r2c7 (marked $ in your grid) has nothing to do with the xy-wing.

--------


On the other hand, columns 4 and 8 contain exactly two "4"s each, forming an "x-wing" pattern (and leading to the elimination of "4" from r3c6 and r3c7.

There is also an xyz wing present (17 in r2c9, 14 in r1c3 and 147 in r2c3) that removes "1" from r2c2, plus a "unique rectangle" of type 1 in r34c12 - but that is a different story altogether.
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arkietech



Joined: 31 Jul 2008
Posts: 1834
Location: Northwest Arkansas USA

PostPosted: Fri May 01, 2009 12:44 pm    Post subject: Reply with quote

I used two steps x=wing 4 and the xyz-wing 147

Good puzzle Very Happy
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Ema Nymton



Joined: 17 Apr 2009
Posts: 89

PostPosted: Fri May 01, 2009 1:16 pm    Post subject: Reply with quote

nataraj wrote:
Ema,

you got to be careful with "rules".

....

On the other hand, columns 4 and 8 contain exactly two "4"s each, forming an "x-wing" pattern (and leading to the elimination of "4" from r3c6 and r3c7.

.


Vielen Dank!

_Slowly_ the light breaks through.

~@:o?
.
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Clement



Joined: 24 Apr 2006
Posts: 1111
Location: Dar es Salaam Tanzania

PostPosted: Fri May 01, 2009 1:43 pm    Post subject: Daily Sudoku: Fri 1-May-2009 VH Reply with quote

I used the following:-
1) UR <38>r34c12
2) APE in cells r2c2&r2c3 no possibility of 1 being in r2c2.
3) X-Wing in 1.
4) Two XY- wings <168> & <478>.
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cgordon



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

PostPosted: Fri May 01, 2009 2:00 pm    Post subject: Reply with quote

I used the x wing (4), xyz (147), and xy (478). But unlike some of the former posters I had no qualms about using the UR on 38 because it was a Type 4 and you have to be pretty smart to use Type 4s !!
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Fri May 01, 2009 9:23 pm    Post subject: Reply with quote

cgordon wrote:
Quote:
But unlike some of the former posters I had no qualms about using the UR on 38 because it was a Type 4 and you have to be pretty smart to use Type 4s !!


Code:
.---------------------.---------------------.---------------------.
| 5      168    14    | 7      3      148   | 2      9      16    |
| 9      178    147   | 2      6      5     | 48     3      17    |
|U38    U13678  2     | 48     9      148   | 468    47     5     |
:---------------------+---------------------+---------------------:
|U38    U38     5     | 6      2      9     | 7      1      4     |
| 7      19     19    | 5      48     48    | 3      6      2     |
| 4      2      6     | 3      1      7     | 9      5      8     |
:---------------------+---------------------+---------------------:
| 6      79     79    | 48     5      2     | 1      48     3     |
| 2      4      3     | 1      78     6     | 5      78     9     |
| 1      5      8     | 9      47     3     | 46     2      67    |
'---------------------'---------------------'---------------------'

I'd be interested to see the grid in which you saw the type 4.
the grid above shows a type 1 UR with respect to {3,8} in r34c12
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA

PostPosted: Fri May 01, 2009 10:45 pm    Post subject: Reply with quote

storm_norm wrote:
cgordon wrote:
Quote:
But unlike some of the former posters I had no qualms about using the UR on 38 because it was a Type 4 and you have to be pretty smart to use Type 4s !!


Code:
.---------------------.---------------------.---------------------.
| 5      168    14    | 7      3      148   | 2      9      16    |
| 9      178    147   | 2      6      5     | 48     3      17    |
|U3-8   U13678  2     | 48     9      148   | 468    47     5     |
:---------------------+---------------------+---------------------:
|U38    U3-8    5     | 6      2      9     | 7      1      4     |
| 7      19     19    | 5      48     48    | 3      6      2     |
| 4      2      6     | 3      1      7     | 9      5      8     |
:---------------------+---------------------+---------------------:
| 6      79     79    | 48     5      2     | 1      48     3     |
| 2      4      3     | 1      78     6     | 5      78     9     |
| 1      5      8     | 9      47     3     | 46     2      67    |
'---------------------'---------------------'---------------------'

I'd be interested to see the grid in which you saw the type 4.
the grid above shows a type 1 UR with respect to {3,8} in r34c12

As posted here, it is also a type 6 because the <3>'s must be on the UR. Therefore, you can remove <8> as shown.

By the same token, it is a (degenerate) Type 4. Choose the floor cells as either in C1 or in R4. Then you can eliminate <8> in the corresponding roof cells in C2 or in R3.

Keith
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Fri May 01, 2009 11:05 pm    Post subject: Reply with quote

ahh,
I see, the type 1 as it stands in the grid can also be looked at as a type 4 and a type 6. I see I see.
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cgordon



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

PostPosted: Sat May 02, 2009 1:31 am    Post subject: Reply with quote

Quote:
As posted here, it is also a type 6 ... By the same token, it is a (degenerate) Type 4.


Forsooth!! Type 6's are surely UR's where the pairs are diagonally orientated. This is a Type 4. There are only two 3s in R3 - so remove the 8's that are with the 3's. And please don't call my Type 4's degenerate!!
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA

PostPosted: Sat May 02, 2009 3:48 am    Post subject: Reply with quote

Quote:
And please don't call my Type 4's degenerate!!

You tell 'em Craig!! People like us are degenerate, not URs. Forsooth!! Laughing
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sudocraz



Joined: 28 Apr 2008
Posts: 53

PostPosted: Sun May 03, 2009 8:40 pm    Post subject: Reply with quote

This was a fun puzzle. My husband and I did and x-wing, then a UR Type 1, then an xywing, and xyz wing and another xy wing.

I believe that the UR was a type 1, because one of those four squares could not be a 38. There was only one square that qualified for this.
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