The New Sudoku Players' Forum

[Yogi]

...54..32....629.5.25.9346.5.138924..4.276.5.2..415.9..3.92.5....2.513.4.58.3..29
I thought this puzzle was interesting. Having done no good in skyscrapers or kites I looked at the forced moves caused by the two possible locations of 3 in Box6. This led to the interesting result that in both cases there would be a locked 67 pair in Boxes 4 & 6, and these cells were all in Rows 4 & 6, forming a 4-cell bivalue chain, and in both outcomes three of the four cells were the same. The resultant two versions of the middle band look like this:

4CellLoop.png (4.17 KiB) Viewed 1153 times

In the upper version the 8 could only go in r6c9 as putting it in r6c7 would cause a Unique Rectangle. Can this 4-cell bivalue loop be used to solve the puzzle, with 3 of its points known?

[JC Van Hay]

N(>1)-"Fish" : only possible for the digits 6, 7, 8.
Among the possible "fishes", the following 2 are sufficient.

Code: Select all

+-------------------+---------------+---------------------+
| 6789   16789  679 | 5      4  78  | 18(7)  3      2     |
| 34     18(7)  34  | 18(7)  6  2   | 9      18(7)  5     |
| 8(7)   2      5   | 18(7)  9  3   | 4      6      18(7) |
+-------------------+---------------+---------------------+
| 5      6(7)   1   | 3      8  9   | 2      4      6(7)  |
| 389    4      39  | 2      7  6   | 18     5      138   |
| 2      678    367 | 4      1  5   | 68(7)  9      3678  |
+-------------------+---------------+---------------------+
| 1467   3      467 | 9      2  478 | 5      178    1678  |
| 69(7)  69(7)  2   | 68(7)  5  1   | 3      8(7)   4     |
| 1467   5      8   | 6-7    3  47  | 16(7)  2      9     |
+-------------------+---------------+---------------------+
"Starfish"{7R2348C7} -> [7r238c4==7r9c7] -> -{7r9c4}; 10 singles
Proof :
||7r2c2 -> r4c9=r3c4=7
||7r2c4
||7r2c8 -> ||7r6c7 -> r4c2=7, XWing(7r38c14)
           ||7r9c7
+----------------+-------------+----------------+
| 9     178   6  | 5    4  78  | 178  3    2    |
| 34    178   34 | 178  6  2   | 9    178  5    |
| 7(8)  2     5  | 178  9  3   | 4    6    1-8  |
+----------------+-------------+----------------+
| 5     6     1  | 3    8  9   | 2    4    7    |
| 3(8)  4     9  | 2    7  6   | 18   5    138  |
| 2     7(8)  37 | 4    1  5   | 6    9    3(8) |
+----------------+-------------+----------------+
| 147   3     47 | 9    2  478 | 5    178  6    |
| 6     9     2  | 78   5  1   | 3    78   4    |
| 147   5     8  | 6    3  47  | 17   2    9    |
+----------------+-------------+----------------+
Kite{8R6C1} -> -{8r3c9}; stte

Can this 4-cell bivalue loop be used to solve the puzzle, with 3 of its points known?

3r6c9 -> 0 solution via, for example, the "Starfish";
8r6c9 -> 1 solution

[Kozo Kataya]

Yes this is an interesting puzzle. As i found below two steps are required.
step1: Because of r8c2<>6 and r9c4<>7, single-digit status of 8 is moved from A to B.
step2: 6-8s can be eliminated, via FISHes, then stte.

Code: Select all

Marked [*] as be false.
A:after del 6and7   B: then stte
*---+---+---*      *---+---+---*
|*8.|..8|8..|      |.*.|..*|8..|
|.8.|8..|.*.|      |.8.|8..|...|
|8..|8..|..8|      |8..|8..|..*|
*---+---+---*      *---+---+---*
|...|.8.|...|      |...|.8.|...|
|8..|...|8.8|      |8..|...|*.8|
|.8.|...|*.8|      {.8.|...|..8|
*---+---+---*      *---+---+---*
|...|..8|.8*|      |...|..8|.*.|
|...|8..|.8.|      |...|*..|.8.|
|..8|...|...|      |..8|...|...|
*---+---+---*      *---+---+---*


Regards kozo