The New Sudoku Players' Forum

[m_b_metcalf]

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 . . 1 . . . . 2 .
 . . 2 . . . . 3 .
 . . 4 5 . . . 1 .
 . . 6 . 7 . . 8 .
 . . 3 . . 1 . 5 .
 . . 9 . . . 4 7 .
 . . 8 . . . . 6 .
 . . 7 . . . . 9 .
 . . 5 . . . . 4 .   moderate

 . . 1 . . . . 2 .
 . . 3 . . . . 4 .
 . . 5 6 . . . 7 .
 . . 4 . 2 . . 8 .
 . . 8 . . 3 . 6 .
 . . 9 . . . 5 3 .
 . . 2 . . . . 1 .
 . . 7 . . . . 9 .
 . . 6 . . . . 5 .   quite hard

[Hajime]

The moderate one basic steps until

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+---------+----------+---------+ 
| 7  39  1| 89   4 36|689  2  5| 
| 5  6   2|1789 19 78| 89  3  4| 
|39  8   4|  5  36  2| 7   1 69| 
+---------+----------+---------+ 
| 4  5   6|  3   7  9| 2   8  1| 
| 8  7   3|  4   2  1| 69  5 69| 
| 2  1   9|  6   8  5| 4   7  3| 
+---------+----------+---------+ 
|39 239  8| 29   5  4| 1   6  7| 
| 6  4   7| 18  13 38| 5   9  2| 
| 1  29  5| 279 69 67| 3   4  8| 
+------------------------------+ 


Then a XY-wing on 3 cells for candidate 1: (1)(1=9)r2c5-(9=8)r1c4-(8=1)r8c4 => (-1)r2c4 (-1)r8c5
stte

[Hajime]

The hard one needs lots of forcing chains according to SE, but if you erase 2 candidates (found by 2 forcing nets)
from the start puzzle (-4)r1c1 and (-2)r2c4. Than, next to basics, only needed:

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Locked Singles [4] |   3.4 |     1 (1)
Turbot-fish    [4] |   4.2 |     7 (7)
XY-Wing        [3] |   4.1 |     2 (2)
XY-chain       [6] |   5.6 |     1 (1)

m(n) means the amount of candidates n erased in m steps, so 7 turbot fishes to erase 7 candidates.
[x] means the number of cells involved, houses for the Locked Singles. x.y is the estimated SE-rating.

[Leren]

Similar to Hajime. Leren

[Hajime]

Forcing nets are not a method in SE, but are they more powerful than forcing chains?