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PostPosted: Wed Sep 13, 2023 8:03 pm 
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The attached image is from puzzlemadness.co.uk, their daily hard killer puzzle dated 12 Sep 2023. This puzzle seemed quite easy, my steps are shown below, but then I get to a point where the puzzle cannot be solved (see image). I have tried this puzzle a number of times and each time, I wind up in an unsolvable position. I am not doing anything fancy and I have triple-checked to make sure that I copied the puzzle properly. What the heck is going on?
Quote:
My steps:
clean up cages
[123] triplet in N1
[689] triplet in N8/9
45 rule, col 1 - r5c2=9
[578] triplet in N4
r9c1 - must be [4]
8 cage in N7 - remove [3]
[125] triplet in N7
13 cage in N7 - r9c3=[7], others are [15]
[15] doublet in N8
r9c2 - must be [2]
r9c9 - must be [3]
[15] doublet in N8
18 cage in N4 - r6c2=[8], others are [46]
r7c3 - only [3] in N7
r4c2 - only [3] on col 2
9 cage in N1 - r3c2 is [6]
r8c2 - only [1] in col 2
8 cage in N7 - r8c3 is 5
r6c2 must be [4]
r6c3 must be [6]
11 cage in N7 - remove [47]
[26] doublet in N8
r7c1 must be 9
r8c1 must be 6
20 cage in N8 - r8c7 must be [2], remove [49]
r9c6 - only [9] in N8
r7c6 - only [4] in N8
[378] triplet in N8
21 cage in N9 - r7c9 is [5]
13 cage in N6 - r6c8 is [5]
21 cage in N1 - r3c3 is [9]
r1c3 must be [4]
r3c3 must be [8]
22 cage N1 - remove [7]
[59] double in N2
r1c9 - only [9] in row 1
r8c9 must be 4
r8c8 must be 9
r3c9 must be 7
27 cage N3 - c2c8 is 3 and r2c9 is 8
17 cage in N6 - r5c8 must be [8]
r9c8 must be 6
r9c7 must be 8

PROBLEM: 11 cage in N3 CANNOT BE SOLVED


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N3Cage11_Issue.jpg
N3Cage11_Issue.jpg [ 181.62 KiB | Viewed 12816 times ]
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PostPosted: Thu Sep 14, 2023 6:22 am 
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Grand Master
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Joined: Wed Apr 23, 2008 6:04 pm
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Location: Lethbridge, Alberta, Canada
Hi Groston

As I've said before, either on this forum or in a direct message to you, it would be much better if you coloured the cages, rather than the nonets, both to make it easier for us to see the structure of the puzzle and for you solving it.

Attachment:
GRoston's Killer Puzzle.jpg
GRoston's Killer Puzzle.jpg [ 32.66 KiB | Viewed 12811 times ]

Rather than trying to work out where you went wrong, here is how I solved it, commenting on the first error I spotted in your diagram.

My solving path:
Prelims

a) 6(3) cage at R1C1 = {123}
b) 21(3) cage at R1C2 = {489/579/678}, no 1,2,3
c) 10(3) cage at R1C6 = {127/126/145/235}, no 8,9
d) 9(3) cage at R3C2 = {126/135/234}, no 7,8,9
e) 22(3) cage at R3C3 = {589/679}
e) 11(3) cage at R3C6 = {128/137/146/236/245}, no 9
f) 11(3) cage at R3C7 = {128/137/146/236/245}, no 9
g) 19(3) cage at R7C1 = {289/379/469/478/568}, no 1
h) 11(3) cage at R7C3 = {128/137/146/236/245}, no 9
i) 8(3) cage at R8C2 = {125/134}
j) 23(3) cage at R9C6 = {689}
k) 27(4) cage at R1C9 = {3789/4689/5679}, no 1,2
l) 29(4) cage at R4C1 = {5789}

1a. Naked triple {123} in 6(3) cage at R1C1, locked for C1 and N1
1b. Naked triple {689} in 23(3) cage at R9C6, locked for R9
1c. Naked quad {5789} in 29(4) cage at R4C1, locked for N4
1d. 22(3) cage at R3C3 = {589/679}, 9 locked for R3
1e. 27(4) cage at R1C9 = {3789/4689/5679}, 9 locked for N3
1f. 45 rule on C1 1 outie R5C2 = 9
1g. 19(3) cage at R7C1 = {469} (hidden triple in C1) -> R9C1 = 4, R78C1 = {69}
1h. 8(3) cage at R8C2 = {125} (only remaining combination), locked for N7
1i. 8 in N7 only in R7C23, locked for R7
1j. 45 rule on R12 2 outies R3C19 = 10 = [28/37]
1k. Killer pair 7,8 in 22(3) cage at R3C3 = {589/679} and R3C9, locked for R3
1l. 45 rule on R89 2 outies R7C19 = 14 = [95] -> R8C1 = 6
1m. 9(3) cage at R3C2 = {126/135/234}
1n. R3C2 = {456} -> no 4,6 in R4C23
1o. 13(3) cage at R9C3 = {157} (only remaining combination) -> R9C3 = 7, R9C45 = {15}, locked for R9 and N8 -> R9C2 = 8, R9C9 = 3
1p. R79C9 = [53] = 8 -> R8C89 = 13 = {49}, locked for R8, 9 locked for N9
1q. R9C6 = 9 (hidden single in R9) -> R9C78 = {68}, locked for N9
1r. 1 in R7 only in R7C78 -> R7C78 = {17}, locked for N9, 7 locked for R7 -> R8C7 = 2
1s. R7C78 = {17} -> R6C8 = 5 (cage total)
1t. R7C456 = {246} (hidden triple in N8) -> 11(3) cage at R7C3 = {236} (only remaining combination) -> R7C3 = 3, R7C6 = 4 (hidden single in R7)
1u. R7C2 = 8 -> R6C3 = 10 = {46} (only remaining combination), locked for R6 and N4
1v. 7 in C2 only in 21(3) cage at R1C2 = {579/678} -> R12C2 = {57/67}, R2C3 = {89}
1w. Naked pair {12} in R45C3, locked for C3 and N4 -> R8C23 = [15]
1x. R4C2 = 3 -> R3C2 + R4C3 = 6 = [42/51]
[That looks to be where you went wrong, you have R3C2 = 6; it’s a 9(3) cage at R3C2, not a 9(2) cage]
1y. 9 in C7 only in R46C7, locked for N6
1z. 27(4) cage at R1C9 = {3789/4689}, 8 locked for N3

2a. 45 rule on C9 3 outies R258C8 = 20 = {389/479}, no 1,2,6
2b. 1,2 in C9 only in R456C9 -> 17(4) cage at R4C9 = {1268} (only remaining combination) -> R5C8 = 8, 1,2,6 locked for N6, 6 locked for C9
2c. R5C8 = 8 -> R28C8 = 12 = [39], R8C9 = 4, R9C78 = [86]
2d. Naked triple {789} in R123C9, 7 locked for N3
2e. 11(3) cage at R3C7 = {146/245} (only remaining combinations) -> R4C8 = 4, R3C78 = [52/61]
2f. Naked triple {379} in R456C7, 7 locked for C7, 3,7 locked for 30(5) cage at R4C7 -> R8C78 = [17]
2g. R456C7 = {379} = 19 -> R5C56 = 11 = {56}, locked for R5 and N5 -> R456C1 = [578], R456C7 = [739]
2h. R4C4 = 9 (hidden single in R4) -> R5C34 + R6C4 = 7 -> R5C4 = 4, R6C5 = {12}
2i. R6C56 = {37} (hidden pair in R6)
2j. 8 in R4 only in R4C56 -> 11(3) cage at R3C6 = {128} -> R3C6 = {12}
2k. R3C1 = 3 (hidden single in R3) -> R3C9 = 7 (step 1j)
2l. 22(3) cage at R3C3 = {589} (only remaining combination), 5 locked for R3
2m. R3C2 = 4, R4C2 = 3 -> R4C3 = 2 (cage sum)
2n. R3C7 = 6, R4C8 = 4 -> R3C8 = 1 (cage sum)
2o. R1C8 = 2 -> R1C67 = 8 = [35], R6C56 = [37]
2p. R1C5 = 4 (hidden single in R1), R1C3 = 6 (hidden single in N1) -> R1C4 = 8 (cage sum)
2q. 22(3) cage at R3C3 = [859]
2r. R6C23 = [64], R1C2 = 7 -> R2C2 = 5

and the rest is naked singles.

Solution:
1 7 6 8 4 3 5 2 9
2 5 9 7 1 6 4 3 8
3 4 8 5 9 2 6 1 7
5 3 2 9 8 1 7 4 6
7 9 1 4 6 5 3 8 2
8 6 4 2 3 7 9 5 1
9 8 3 6 2 4 1 7 5
6 1 5 3 7 8 2 9 4
4 2 7 1 5 9 8 6 3


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PostPosted: Thu Sep 14, 2023 2:28 pm 
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Thanks for sharing. I did the puzzle, yet again, but this time I solved it. I must have made the same sort of stupid mistake every other time. Sigh...


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