## Stuck seemingly having to guess

Post the puzzle or solving technique that's causing you trouble and someone will help

### Stuck seemingly having to guess

Hello. I have looked at different techniques but cannot pare this puzzle down further. An online solver (sudoku-solver.com) told me there were no logical solutions - i.e. trial and error. I am hoping that is not the case, and that it is just a guessing game.

It is from the ticbits Sudoku app, expert level.

Many thanks.

sudokupik1.jpg (71.58 KiB) Viewed 1515 times
User16

Posts: 5
Joined: 17 December 2014

### Re: Stuck seemingly having to guess

There is a remote pair on 89 (a chain of cells containing pencil marks for 8 and 9) that allows further progress.

You can certainly solve this puzzle without guessing/trial and error. However, it will take a couple of techniques at least as difficult as remote pair (or one quite a bit more advanced technique).

JasonLion
2017 Supporter

Posts: 640
Joined: 25 October 2007
Location: Silver Spring, MD, USA

### Re: Stuck seemingly having to guess

There are only 2 solutions for the digit 8; stte
JC Van Hay

Posts: 719
Joined: 22 May 2010

### Re: Stuck seemingly having to guess

User16 wrote:Hello. I have looked at different techniques but cannot pare this puzzle down further. An online solver (sudoku-solver.com) told me there were no logical solutions - i.e. trial and error. I am hoping that is not the case, and that it is just a guessing game.

Using only easy techniques (biv-chain is the super-symmetric view of Nice Loop or AIC):
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`finned-x-wing-in-columns: n8{c9 c4}{r3 r4} ==> r4c6 ≠ 8, r4c5 ≠ 8biv-chain[2]: r9n8{c5 c1} - c2n8{r8 r5} ==> r5c5 ≠ 8biv-chain[2]: c8n8{r6 r2} - r3n8{c9 c4} ==> r6c4 ≠ 8singles ==> r6c4 = 1, r5c7 = 1, r4c7 = 6naked-triplets-in-a-row: r4{c4 c5 c6}{n3 n4 n7} ==> r4c3 ≠ 7hidden-single-in-a-block ==> r6c3 = 7biv-chain[3]: r2c8{n8 n9} - c6n9{r2 r7} - b8n8{r7c6 r9c5} ==> r2c5 ≠ 8stte`
denis_berthier
2010 Supporter

Posts: 1261
Joined: 19 June 2007
Location: Paris

### Re: Stuck seemingly having to guess

Here's a solution that involves no guesswork:

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`*--------------------------------------------------------------*| 4     9     8      | 2     1     5      | 7     3     6      || 7     1     6      | 34    489   389    | 2     89    5      || 2     3     5      |c89    67    67     | 4     1    b89     ||--------------------+--------------------+--------------------|| 1689  2     179    | 34    467-8 367-8  | 16    5    a89     || 5     68    3      |d189   689   2      | 16    7     4      || 1689  4     179    |d18    5     678    | 3     89    2      ||--------------------+--------------------+--------------------|| 3     5     4      | 7     2     89     | 89    6     1      || 1689  68    19     | 5     3     4      | 89    2     7      || 89    7     2      | 6     89    1      | 5     4     3      |*--------------------------------------------------------------*`

Follow the cells marked abcd and you see that at least 1 of r4c9 and r56c4 must be 8 so 8 can be removed from r4c56. This move is called a Grouped Skyscraper.

Code: Select all
`*--------------------------------------------------------------*| 4     9     8      | 2     1     5      | 7     3     6      || 7     1     6      | 34    489   389    | 2    b89    5      || 2     3     5      |d89    67    67     | 4     1    c89     ||--------------------+--------------------+--------------------|| 1689  2     179    | 34    467   367    | 16    5     89     || 5     68    3      | 189   689   2      | 16    7     4      || 1689  4     179    | 1-8   5     678    | 3    a89    2      ||--------------------+--------------------+--------------------|| 3     5     4      | 7     2     89     | 89    6     1      || 1689  68    19     | 5     3     4      | 89    2     7      || 89    7     2      | 6     89    1      | 5     4     3      |*--------------------------------------------------------------*`

Follow the cells marked abcd and you see that at least 1 of r6c8 and r3c4 must be 8 so 8 can be removed from r6c4. This move is called a 2 Stringed Kite.

Code: Select all
`*--------------------------------------------------------------*| 4     9     8      | 2     1     5      | 7     3     6      || 7     1     6      | 34    489   389    | 2     89    5      || 2     3     5      | 89    67    67     | 4     1     89     ||--------------------+--------------------+--------------------|| 189   2     19     | 34    47    37     | 6     5     89     || 5    a68    3      | 89    69-8  2      | 1     7     4      || 689   4     7      | 1     5     68     | 3     89    2      ||--------------------+--------------------+--------------------|| 3     5     4      | 7     2     89     | 89    6     1      || 1689 b68    19     | 5     3     4      | 89    2     7      ||c89    7     2      | 6    d89    1      | 5     4     3      |*--------------------------------------------------------------*`

A bit further on follow the cells marked abcd and you see that at least 1 of r5c2 and r9c5 must be 8 so 8 can be removed from r5c5. This is another 2 Stringed Kite.

Code: Select all
`*--------------------------------------------------------------*| 4     9     8      | 2     1     5      | 7     3     6      || 7     1     6      | 34   b489   38-9   | 2    a89    5      || 2     3     5      | 89    67    67     | 4     1     89     ||--------------------+--------------------+--------------------|| 189   2     19     | 34    47    37     | 6     5     89     || 5     68    3      | 89    69    2      | 1     7     4      || 689   4     7      | 1     5     68     | 3     89    2      ||--------------------+--------------------+--------------------|| 3     5     4      | 7     2    d89     | 89    6     1      || 1689  68    19     | 5     3     4      | 89    2     7      || 89    7     2      | 6    c89    1      | 5     4     3      |*--------------------------------------------------------------*`

Next follow the cells marked abcd and you'll find that at least one of r2c8 or r7c6 must be 9, so 9 can be removed from r2c6. This move is called a W Wing.

The puzzle should then solve easily.

Leren
Leren

Posts: 3368
Joined: 03 June 2012

### Re: Stuck seemingly having to guess

Thank you so very much! I will study the replies and, I suspect, learn a lot!
User16

Posts: 5
Joined: 17 December 2014