Let's recap... This is the state you can achieve with basic techniques:
- Code: Select all
3 58 67 | 149 19 56 | 2 18 1478
1 9 4 | 7 2 8 | 3 6 5
58 2 67 | 14 3 56 | 478 9 1478
-------------------+-------------------+------------------
7 1 8 | 3 4 9 | 5 2 6
6 3 9 | 2 5 7 | 48 18 148
2 4 5 | 8 6 1 | 9 7 3
-------------------+-------------------+------------------
*58 6 2 |*15 7 3 | 18 4 9
9 -78 3 | 16 *18 4 | 1678 5 2
4 578 1 | 569 89 2 | 678 3 78
There is a simple xy-wing in r7c14 and r8c25 => r8c2<>8, therefore r8c2=7...
Pyrrhon's "simple forcing loop" works like this:
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3 *58 67 | 149 *19 56 | 2 *18 1478
1 9 4 | 7 2 8 | 3 6 5
58 2 67 | 14 3 56 | 478 9 1478
-------------------+-------------------+------------------
7 1 8 | 3 4 9 | 5 2 6
6 3 9 | 2 5 7 | 48 18 148
2 4 5 | 8 6 1 | 9 7 3
-------------------+-------------------+------------------
58 6 2 | 15 7 3 | 18 4 9
9 7 3 | 16 18 4 | 168 5 2
4 *58 1 | 569 *89 2 | 678 3 78
[r1c5]-1-[r1c8]-8-[r1c2]=58=[r9c2]-8-[r9c5]=9=[r1c5]
It follows that:
r1c49=1|8 (together with r1c8) will force r1c5=9 & r1c2=5 => r9c2=8 => r9c5=9, so r1c4<>1, r1c9<>1|8
r9c79=8 will force r9c5=9 & r9c2=5 => r1c2=8 => r1c8=1 => r1c5=9, so r9c79<>8
Alternatively, you can work on the following turbot chain:
- Code: Select all
3 *58 67 | 149 19 56 | 2 *18 1478
1 9 4 | 7 2 8 | 3 6 5
*58 2 67 | 14 3 56 | 478 9 1478
-------------------+-------------------+------------------
7 1 8 | 3 4 9 | 5 2 6
6 3 9 | 2 5 7 |-48 *18 148
2 4 5 | 8 6 1 | 9 7 3
-------------------+-------------------+------------------
*58 6 2 | 15 7 3 |*18 4 9
9 7 3 | 16 18 4 | 168 5 2
4 58 1 | 569 89 2 | 678 3 78
[r5c7]-8-[r7c7]=8=[r7c1]=8=[r3c1]=8=[r1c2]-8-[r1c8]=8=[r5c8]-8-[r5c7]
It follows directly that r5c7<>8 and thus r5c7=4... And then a naked quad on r3 and an x-wing on 8 solves it...