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Susume's jellyfish trick

 
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Joined: 21 Apr 2006
Posts: 536

PostPosted: Mon Nov 03, 2008 2:04 pm    Post subject: Susume's jellyfish trick Reply with quote

In the thread A Pure Jellyfish Collection on the Players forum susume noticed (some posts down), that in puzzles, where 16 numbers are given in a 4x4 jellyfish pattern, it can be easy to find a jellyfish without pencilmarks.

Since the pattern of the current game (0058) of the Patterns Game has this property, you can find new examples there, e.g.
Code:
 +-------+-------+-------+
 | . . 5 | . . . | 8 . . |
 | . 1 . | 4 . 5 | . 6 . |
 | 7 . . | . . . | . . 1 |
 +-------+-------+-------+
 | . 5 . | 9 . 6 | . 2 . |
 | . . . | . . . | . . . |
 | . 6 . | 1 . 2 | . 4 . |
 +-------+-------+-------+
 | 4 . . | . . . | . . 9 |
 | . 2 . | 6 . 9 | . 1 . |
 | . . 1 | . . . | 3 . . |
 +-------+-------+-------+ Tarek

There are givens in r2468c2468, but 378 is missing there.
With the 3 in r9c7 for these columns 2468 only rows 1357 remain, which can have a 3. So there must be a jellyfish (or something simpler) there for number 3. (The same holds for rows 2468, where 3 is restricted to columns 1359, giving the same eliminations)

Similar for 7 and 8.
This means, that the cells marked x cannot have 378.
Code:
 +-------+-------+-------+
 | x . 5 | . x . | 8 . x |
 | . 1 . | 4 . 5 | . 6 . |
 | 7 . x | . x . | x . 1 |
 +-------+-------+-------+
 | x 5 x | 9 x 6 | x 2 x |
 | . . . | . . . | . . . |
 | x 6 x | 1 x 2 | x 4 x |
 +-------+-------+-------+
 | 4 . x | . x . | x . 9 |
 | . 2 . | 6 . 9 | . 1 . |
 | x . 1 | . x . | 3 . x |
 +-------+-------+-------+

Then in r7c3 6 remains as a naked single and the puzzle is solved.


In the same way this puzzle can be solved (here the jellyfish leave a naked pair):
Code:
 +-------+-------+-------+
 | . . 1 | . . . | 2 . . |
 | . 3 . | 4 . 5 | . 6 . |
 | 6 . . | . . . | . . 4 |
 +-------+-------+-------+
 | . 5 . | 6 . 2 | . 7 . |
 | . . . | . . . | . . . |
 | . 2 . | 7 . 3 | . 4 . |
 +-------+-------+-------+
 | 8 . . | . . . | . . 9 |
 | . 6 . | 2 . 7 | . 3 . |
 | . . 3 | . . . | 6 . . |
 +-------+-------+-------+ JPF
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