Finally worked out how to unlock this one.
1. From puzzle pic above - two 7's in N7.
-7 in r9c2=>r8c9=>r1c78-> no 7 in r1c1 [edit:typo]
-7 in r8c1 -> no 7 in r1c1
->no 7 in r1c1
2. each 8 on D\ eliminates 8 from r1c3
-8 in r7c7=>r5c9=>r46c3 -> no 8 in r1c3
-8 in r5c5 =>r46c3-> no 8 in r1c3
-8 in r1c1, r2c2 or r3c3 -> no 8 in r1c3
-> no 8 in r1c3 [edit:typo]
r1c1 = {38}, r1c3 ={13}
3. 7 in r1 locked in n3 -> no 7 elsewhere n3-> 7 in c9 in r58c9.
3a. 7 in r8c9 =>r9c2 => r3c3 -> no 7 in r5c23
3b. 7 in r5c9 -> no 7 in r5c23
-> no 7 in r5c23 [edit2:this step added]
This leaves the puzzle in the following position
Code: Select all
.------------------.------------------.------------------.
| 38 4 13 | 6 5 2 | 1378 378 9 |
| 5 378 9 | 4 378 1 | 6 2 38 |
| 238 236 13678| 9 378 38 | 5 4 138 |
:------------------+------------------+------------------:
| 9 1 378 | 2 4 38 | 378 6 5 |
| 23678 238 38 | 1 368 5 | 4 9 378 |
| 4 5 368 | 7 36 9 | 38 1 2 |
:------------------+------------------+------------------:
| 368 9 4 | 5 2 7 | 138 38 1368 |
| 367 36 2 | 8 1 4 | 9 5 367 |
| 1 78 5 | 3 9 6 | 2 78 4 |
'------------------'------------------'------------------'
4. A contradiction chain shows that 3 cannot go in r1c3.
3 in r1c3=>8 r1c1=>1 r1c7 => 7 r1c8 also 3 in r7c7 (from D\ and r1c7) but this leaves 8 in both r79c8
->r1c3 = 1 [edit2: typo]
From here
Code: Select all
.------------------.------------------.------------------.
| 38 4 1 | 6 5 2 | 378 378 9 |
| 5 378 9 | 4 378 1 | 6 2 38 |
| 238 236 3678 | 9 378 38 | 5 4 1 |
:------------------+------------------+------------------:
| 9 1 378 | 2 4 38 | 378 6 5 |
| 23678 238 38 | 1 368 5 | 4 9 378 |
| 4 5 368 | 7 36 9 | 38 1 2 |
:------------------+------------------+------------------:
| 368 9 4 | 5 2 7 | 1 38 368 |
| 367 36 2 | 8 1 4 | 9 5 367 |
| 1 78 5 | 3 9 6 | 2 78 4 |
'------------------'------------------'------------------'
5.r5c5<>8 since leaves 8 for n12 in r3 -> r4c6 = 8
6.8 in D\ only in n1 -> no 8 in r3c1
7. two 3's in D/: cross-over -> no 3 in r5c2 or r2c2
the rest unravels from there
[edit2:steps 5-7 added]