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A "Turbot Fish" example

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David Bryant

Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado

Posted: Sun Nov 06, 2005 6:10 pm Post subject: A "Turbot Fish" example

This puzzle appeared in the Rocky Mountain News on Saturday, November 5. It contains a good example of the "turbot fish" formation.

Code:

5 . . . . 4 . . 2
3 . . . . . . 6 .
. . 8 5 . . 4 . .

8 . . . 9 . 6 . 4
. . . 1 8 6 . . .
1 . 3 . 2 . . . 5

. . 4 . . 9 2 . .
. 1 . . . . . . 6
6 . . 2 . . . . 7

After a series of mostly routine moves one arrives at this position.

Code:

5 7/9 6 8/9 *1/3* 4 1/3/8 3/7/8 2
3 4 1 8/9 7 2 5 6 8/9
2 7/9 8 5 6 *1/3* 4 3/7 *1/9*

8 2 7 3 9 5 6 1 4
4 5 9 1 8 6 7 2 3
1 6 3 4 2 7 8/9 8/9 5

7 3/8 4 6 *1/3/5* 9 2 3/5/8 *1/8*
9 1 2 7 4/5 3/8 3/8 4/5 6
6 3/8 5 2 1/3/4 1/3/8 . . 7

The key to further progress lies in the chain of 1/~1 cells marked with "*"s in this grid. We can see that r7c5 cannot be a "1" because if it is a contradiction cannot be avoided. So the "1" in row 7 must appear at r7c9, and the rest of the puzzle is easily resolved.

This formation is a type of "turbot fish," which has been well analyzed by "Nick70" on the sudoku.com forum. dcb

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