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VH+ by gsf (game 0037)

 
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ravel



Joined: 21 Apr 2006
Posts: 536
PostPosted: Fri Jun 06, 2008 7:15 am    Post subject: VH+ by gsf (game 0037) Reply with quote
Code:
. 1 . . . . . . 8
2 . 3 . . . . . .
. 4 . . 1 . 5 . .
. . . 3 . . . . 4
. . 1 . 5 . . 6 .
. . . . . 1 7 . .
. . 5 . . 7 3 . .
. . . . 4 . . 2 .
9 . . 8 . . . . 6 gsf

>>>play online
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Earl



Joined: 30 May 2007
Posts: 677
Location: Victoria, KS
PostPosted: Fri Jun 06, 2008 6:24 pm    Post subject: VH+ Reply with quote
Color <8>, color <9>, then an xy-chain eliminates <5> in R2C4 to finish.

Earl
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Asellus



Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA
PostPosted: Sat Jun 07, 2008 11:00 pm    Post subject: Reply with quote
A different route had some interesting scenery:

(1) Skyscraper on <8>
Then, killing off <9>s down c5...
(2) Kite (or Sashimi Swordfish): r2c5<>9
(3) XY Wing, pivot r3c1: r1c5<>9
(4) 29 UR: r4c5<>9
and arriving here
Code:
+-------------+---------------+------------+
| 56  1   p79 | 2   B37  45   | 46  379  8 |
| 2   59   3  | 569  78  4589 | 46  79   1 |
|A67  4    8  |p69   1  p39   | 5   379  2 |
+-------------+---------------+------------+
| 57  589  79 | 3    28  6    | 29  1    4 |
| 4   89   1  | 7    5   28   | 29  6    3 |
| 3   6    2  | 4    9   1    | 7   8    5 |
+-------------+---------------+------------+
| 8   2    5  | 1    6   7    | 3   4    9 |
| 1   3    6  | 59   4   59   | 8   2    7 |
| 9   7    4  | 8    23  23   | 1   5    6 |
+-------------+---------------+------------+

where there is an interesting final step. There are two seemingly useless XY Wings that share a pincer at r1c3: one pivots at "A" with pincer r3c4 (this was used at Step 3 above) and one pivots at "B" with pincer r3c6. Because the <9>s in r3c46 are weakly linked, r1c3 must be <9>.

Using the pincer strong links, this can be seen as a very short AIC:
(9)r1c3=(9)r3c4-(9)r3c6=(9)r1c3; r1c3=9

Because XY Wings are short XY Chains, this could also be seen in more detail as an XY Chain AIC:
(9=7)r1c3-(7=6)r3c1-(6=9)r3c4-(9=3)r3c6-(3=7)r1c5-(7=9)r1c3; r1c3=9
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ravel



Joined: 21 Apr 2006
Posts: 536
PostPosted: Sun Jun 08, 2008 10:39 am    Post subject: Reply with quote
Nice find, Asellus (i also missed the 29 UR).

The short way to solve it is with the skyscraper for 8 in r35 (r2c2<>8, r4c3<>8) and the w-wing 79 in r1c3/r2c8 with strong link for 7 in r3 (r1c8<>9, r2c2<>9).
That one is present in the grid above as well as an xyz-wing 59/569/69 in r23 to eliminate 9 from r2c6 ("useless").
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