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Hello. After the great advice for my first post, I have spent a long time trying to use Flamboyant Wingnut Interboxinal and so-on methods to solve this (I am not entirely sure that is the right name!).

So far I solved one number, E8 to 6, and i just cannot find anything else. This app has a very big gap between hard, where pointing pairs and so on will lead to a result, and expert which throws you in the deep end of these more obscure and difficult techniques. If there is a better graduated app/source out there please let me know.

Thank you again!

I see a couple of finned fish, but after that it get far more difficult. If you are having trouble spotting the finned fish, it seems unlikely you will be able to finish.

My Sudoku apps, see www . EnjoySudoku . com, have a rather large number of difficulty levels (17), with much more gradual steps between them than what you describe.

Code: Select all

*--------------------------------------------------------------------------------*
| 289     3       28       | 5       1       4        | 279     27      6        |
| 2569    7       256      | 2369    23      2-6      | 14      14      8        |
|b269     4       1        |a269     7       8        | 259     3       259      |
|--------------------------+--------------------------+--------------------------|
| 12578   1258    2578     | 4       6       19       | 12579   1257    3        |
| 4       15      9        | 23      23      7        | 8       6       15       |
| 3       6       27       | 8       5       19       | 12479   1247    1249     |
|--------------------------+--------------------------+--------------------------|
| 2568    9       3        | 1       48      256      | 2456    245     7        |
|c1256    125     4        | 7       9      d256      | 3       8       125      |
| 125678  1258    25678    | 2-6     48      3        | 12456   9       1245     |
*--------------------------------------------------------------------------------*

Your next move would be a Skyscraper in 6's.

Note that there are 2 6's in Rows 3 and 8 in the cells marked a,b,c & d.

If you assume that the 6 in cell a is False => 6 in b is True => 6 in c is False => 6 in d is True.

If you assume that the 6 in cell d is False => 6 in c is True => 6 in b is False => 6 in a is True.

The net result of this is that at least 1 of the 6's in cells a and d must be True.

Since r2c6 and r9c4 can see both of these cells then you can remove the 6's from those cells.

Several basic eliminations should get you to here:

Code: Select all

*--------------------------------------------------------------------------------*
| 289     3       28       | 5       1       4        | 279     27      6        |
| 569     7       56       | 69      3       2        | 14      14      8        |
| 269     4       1        | 69      7       8        | 259     3       259      |
|--------------------------+--------------------------+--------------------------|
| 12578   1258    2578     | 4       6       19       | 12579   1257    3        |
| 4      *15      9        | 3       2       7        | 8       6      *15       |
| 3       6       27       | 8       5       19       | 12479   1247    1249     |
|--------------------------+--------------------------+--------------------------|
| 2568    9       3        | 1       48      56       | 2456    245     7        |
|f1256   *125     4        | 7       9       56       | 3       8      *125      |
| 15678   58-1    5678     | 2       48      3        | 1456    9       145      |
*--------------------------------------------------------------------------------*

There is a finned XWing in 1's in r58/c29 with a fin at r8c1, which removes the 1 from r9c2. Hopefully you understand how finned XWings work.

The next move is not the simplest, but it solves a cell and makes the solution shorter.

Code: Select all

*--------------------------------------------------------------------------------*
| 289     3       28       | 5       1       4        | 279     27      6        |
| 569     7       56       | 69      3       2        | 14      14      8        |
| 269     4       1        | 69      7       8        | 259     3      g29-5     |
|--------------------------+--------------------------+--------------------------|
| 12578   1258    2578     | 4       6       19       | 12579   1257    3        |
| 4      b15      9        | 3       2       7        | 8       6      a15       |
| 3       6       27       | 8       5       19       | 12479   1247   f1249     |
|--------------------------+--------------------------+--------------------------|
| 2568    9       3        | 1       48      56       | 2456    245     7        |
| 1256    125     4        | 7       9       56       | 3       8       125      |
| 15678  c58      5678     | 2      d48      3        | 1456    9      e145      |
*--------------------------------------------------------------------------------*

The chain notation for this move is (5=1) r5c9 - (1=5) r5c2 - (5=8) r9c2 - (8=4) r9c5 - (4) r9c9 = (4-9) r6c9 = (9) r3c9

Basically what it says that if you assume 5 is False in r5c9 and follow the True/False implications in cells abcdefg then you must conclude that 9 is True in r3c9, in particular 5 is False in r3c9.

Obviously if 5 is True in r5c9 then 5 is False in r3c9. So, since 5 can only be True or False in r5c9 it can be removed from r3c9.

This solves r3c7 = 5 and leads you to here:

Code: Select all

*--------------------------------------------------------------------------------*
| 289     3       28       | 5       1       4        | 279     27      6        |
| 569     7       56       | 69      3       2        | 14      14      8        |
|b269     4       1        | 69      7       8        | 5       3      a29       |
|--------------------------+--------------------------+--------------------------|
| 12578   1258    2578     | 4       6       19       | 1279    1257    3        |
| 4       15      9        | 3       2       7        | 8       6       15       |
| 3       6       27       | 8       5       19       | 12479   1247    1249     |
|--------------------------+--------------------------+--------------------------|
|c2568    9       3        | 1       48      56       |d246    e245     7        |
| 1256    125     4        | 7       9       56       | 3       8       15-2     |
| 15678   58      5678     | 2       48      3        | 146     9       145      |
*--------------------------------------------------------------------------------*

This move is a grouped Skyscraper in 2's. The logic is similar to the previous Skyscraper except that there are 3 2's in Row 7.

Basically this shows that at least one of cells a, d or e must be 2. Since r8c9 can see all of these cells the 2 there can be removed.

Only basic moves are then required to solve the puzzle.

Take a look at the following site which gives explanations of the solving methods I've used : http://hodoku.sourceforge.net/en/techniques.php

On that site the second last move is an AIC type 2. The grouped skyscraper can also be thought of as a Sashimi finned XWing.

Leren