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Aug 21 VH

 
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Clement



Joined: 24 Apr 2006
Posts: 1056
Location: Dar es Salaam Tanzania

PostPosted: Sat Aug 21, 2021 10:51 am    Post subject: Aug 21 VH Reply with quote

Code:

+-----------------+----------------------+------------------+
| 8      3     45 | 245     245      7   | 9      1      6  |
| 9      7     45 | 6       1458     124 | 3      24     28 |
| 2      1     6  | 9       8-4      3   | 78    a47     5  |
+-----------------+----------------------+------------------+
| 7      2     9  | 3       6        5   | 4      8      1  |
| 6      8     1  | 24      9        24  | 5      3      7  |
| 5      4     3  | 1       7        8   | 2      6      9  |
+-----------------+----------------------+------------------+
| 3      5     8  | 7       12       12  | 6      9      4  |
| 14     9     7  | 45      3        6   | 18     25     28 |
| 14     6     2  | 8      c45       9   | 17    b57     3  |
+-----------------+----------------------+------------------+

XY-Wing pivoted in r9c8: (4=7)r3c8 - (7=5)r9c8 - (5=4)r9c5 => - 4r3c5; stte
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Mogulmeister



Joined: 03 May 2007
Posts: 868

PostPosted: Tue Aug 24, 2021 8:40 am    Post subject: Extended pincers Reply with quote

Nice one Clement.

Sometimes when you are looking at a puzzle for XY wings you find one but it doesn't make any eliminations.

There is also a 2,4,5 XY Wing at r28c8 and r8c4.

As it stands, no eliminations can be made because the pincers at r2c8 and r8c4 point to r2c4 which is a solved square (6).

No need to abandon these "dead" XY Wings straightaway. See if the pincers can be extended.

In this case the pincers are for 4 but if you extend r2c8 across to r2c3 then that 4 becomes a pincer for 5. Do the same r8c4 => r9c5 also becomes 5.

You now have pincers for 5 at r2c3 and r9c5 which eliminates 5 at r2c5.

On this occasion, this doesn't solve the whole puzzle but is a useful technique when working with XY wings.
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