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Hi all

Here's another puzzle for which Ruud tended to be (in)famous for: killer puzzles without 2 cell cages. One 5-cell cage, four 4-cell cages and 20 3-cell cages to keep you busy. I know udosuk just did one, but this was already made before i knew that.

Assassin 125



SS-Score: 1.09
Estimated rating: 1.0

PS-code:

Solution:

Enjoy

Para

Hi all

I'm posting a second puzzle to encourage some other players on the forum to try a killer too. It's an easy killer, prob like a times killer although i have never done one of those. There will also be a V2 out later this week.

Assassin 125V0 "Newbie killer"


SS-score: 0.69
Estimated rating: 0.5-0.75

PS-Code:

Solution:

For everyone new trying this, I hope you enjoyed it. Don't shy away from trying the V1.

Para

Thanks for this week's Assassin! And thanks for posting it so soon since else Andrew would have posted the first walkthrough.

I probably took a technical harder way than necessary but I couldn't resist using a Killer triple which I disguised as a Killer pair (step 1d).

A125 Walkthrough:

1. C123 !
a) 7(3) = {124} locked for N4
b) Innies+Outies C1: -3 = R46C2 - R9C1 -> R6C2 = (35) and R4C2 <> 4; R9C1 = (789)
c) 7(3) = {124} -> 4 locked for C1
d) ! Killer pair (12) locked in 19(4) + R45C1 for C1
e) 16(3) = 3{58/67} -> 3 locked for C1+N1
f) 9(3) = {126} locked for N1
g) 16(3) = {358} locked for C1+N1
h) Innies+Outies C1: -3 = R46C2 - R9C1; R9C1 = (79) -> R46C2 = 4/6(2) = 1{3/5} -> R4C2 = 1
i) Hidden Single: R2C3 = 1 @ N1

2. C123
a) 9(3) = {126} -> 2,6 locked for C2
b) 7(3) = {124} -> 2 locked for C1
c) 1 locked in Innies N7 = 12(3) = 1{29/47/56} -> R7C3 = (245)
d) Innies N47 = 11(2) = [65/92] since {47} blocked by R13C3 = (479)
e) 15(3) @ N4 must have one of (235) -> R4C4 = (235)
f) 15(3) @ N4 = {249/267/456} <> 3 because R4C3 = (69); R3C3 <> 9

3. N12 !
a) Innies N12 = 11(2) = {47} locked for R3
b) 9 locked in 24(4) @ N1 for R1 -> 24(4) = 9{267/348/357/456} <> 1 since R1C23 = (479); R12C4 <> 4,7,9
c) 9 locked in 19(3) @ N2 = 9{28/37/46} <> 5
d) 1 locked in 11(3) @ N2 for R1; 11(3) = 1{28/37/46} <> 5
e) ! 5 locked in 24(4) @ N2 for C4 -> 24(4) = 59{37/46}
f) R4C4 = 2, R4C1 = 4, R5C1 = 2

4. N3689
a) 2 locked in 16(3) @ R6 = 2{59/68}
b) 1 locked in 11(3) @ N6 for R5 = 1{37/46}
c) Innies N89 = 17(2) = {89} locked for R7
d) Hidden Single: R6C4 = 1 @ C4
e) 15(3) = {159} -> R7C3 = 5, R7C4 = 9
f) R7C7 = 8
g) 18(3) <> 1
h) Hidden Single: R3C9 = 1 @ C9
i) 17(3) = {278/458/467} <> 3,9 because R3C6 = (47)

5. N1346
a) Innie N47 = R4C3 = 6
b) Cage sum: R3C3 = 7
c) 24(4) = {4569} -> 4 locked for R1, 6 locked for C4+N2
d) 14(3) = 5{27/36} -> 5 locked for N3
e) R3C6 = 4
f) 17(3) = {467} because (58) only possible @ R4C6 -> R3C7 = 6, R4C6 = 7
g) R4C7 = 3
h) 19(4) = {1459} since R4C89 = (589) -> R2C9 = 4, {59} locked for R4+N6
i) 11(3) = {137} -> 7 locked for R5+N6
j) R6C7 = 4 -> R6C6 = 9
k) 20(3) @ N3 = {389} -> R2C7 = 9, {38} locked for C8+N3

6. R789
a) R6C1 = 7, R9C1 = 9
b) 18(3) = {279} -> R9C2 = 7, R9C3 = 2
c) 19(3) = {478} because (56) only possible @ R9C5 -> R8C4 = 7; {48} locked for R9+N8
d) 8(3) = {125} -> R8C5 = 5; {12} locked for R7+N8
e) 13(3) = {247} -> R8C7 = 2, R8C8 = 4, R7C8 = 7

7. Rest is singles.

Rating: (Hard) 1.0. I nearly used a Killer triple.

Thanks Para

I think your V0 is a first, but welcome addition to the forum. Solved it on my lunch break today, about 20 minutes. Yes, it's about a Times Deadly rating, but a nice quick diversion.

I think it was enxio and Ed (maybe wrong) who first issued a challenge to each other. One would try to solve a killer and the other a samurai. You've given them a golden opportunity!

Since Afmob had already posted a walkthrough for A125 while I was still setting up and colouring my diagrams, I thought I would try A125 V0 first.

Thanks Para for an excellent Newbie Killer!

This puzzle can be done by either insertion or elimination solving. Which way did you do it Ronnie? Are you going to post your walkthrough?

Since it was described as being about Times Deadly standard, I decided to do it using insertion solving. I haven't done a Times puzzle but it took me longer than I usually take for the Weekly Extreme Killers on http://www.sudoku.org.uk, which I think are supposed to be around Times Deadly level, so I'll rate A125 V0 at 0.75; it's probably easier and quicker using elimination solving.

Here is my walkthrough using insertion solving. I'll leave it hidden even after future puzzles appear.

That wasn't going to happen this time. I found A125 hard to get into until I realised that I'd been looking at the innie-outie difference in step 9 the wrong way round. Once I spotted my mistake the rest of this puzzle wasn't too difficult.

I'll rate A125 at Easy 1.25 the way that I solved it.

Here is my walkthrough.

Prelims

a) 9(3) cage in N1 = {126/135/234}, no 7,8,9
b) 11(3) cage in N2 = {128/137/146/236/245}, no 9
c) 19(3) cage in N2 = {289/379/469/478/568}, no 1
d) 20(3) cage in N3 = {389/479/569/578}, no 1,2
e) 7(3) cage in N4 = {124}, locked for N4
f) 11(3) cage in N6 = {128/137/146/236/245}, no 9
g) 21(3) cage at R6C6 = {489/579/678}, no 1,2,3
h) 8(3) cage in N8 = {125/134}, 1 locked for N8

1. 45 rule on N1 3 innies R1C23 + R3C3 = 20 = {389/479/569/578}, no 1,2

2. 45 rule on N3 3 innies R23C9 + R3C7 = 11 = {128/137/146/236/245}, no 9

3. 45 rule on N89 2 innies R7C47 = 17 = {89}, locked for R7
3a. 19(3) cage in N8 = {379/469/478/568} (cannot be {289} which clashes with R7C4), no 2
3b. Killer pair 8,9 in R7C4 and 19(3) cage, locked for N8
3c. R789C9 cannot be {189} which clashes with R7C7, no 1
3d. Min R7C4 = 8 -> max R6C4 + R7C3 = 7, no 7,8,9

4. 45 rule on N36 2 innies R36C7 = 10 = [19/28/37/46/64], no 5, no 7,8 in R3C7

5. 45 rule on N12 2 innies R3C36 = 11 = {38/47/56}/[92], no 1,9 in R3C6
5a. R3C36 = 11 -> R3C67 cannot be 11 because of overlap -> no 6 in R4C6
5b. Max R3C67 = 14 -> min R4C6 = 3

6. 45 rule on N47 2 innies R47C3 = 11 = [56/65/74/83/92], no 3 in R4C3, no 1 in R7C3
6a. R47C3 = 11 -> R34C3 cannot be 11 because of overlap -> no 4 in R4C4
6b. Min R34C3 = 8 -> max R4C4 = 7
6c. Min R7C34 = 10 -> max R6C4 = 5

7. 45 rule on N9 3 innies R7C7 + R9C78 = 14, min R7C7 = 8 -> max R9C78 = 6, no 6,7,8,9

8. 45 rule on R1234 4 innies R4C1257 = 16 = {1249/1258/1267/1348/1456/2347} (cannot be {1357/2356} because R4C12 must have two of 1,2,4)
8a. 9 of {1249} must be in R4C5, 1,2,4 of the other combinations must be in R4C12 -> no 1,2,4 in R4C5

9. 45 rule on C1 1 innie R9C1 = 2 outies R46C2 + 3
9a. Min R46C2 = 4 -> min R9C1 = 7
9b. Max R9C1 = 9 -> max R46C2 = 6, no 4 in R4C2, no 6,7,8,9 in R6C2
9c. 4 in N4 locked in R45C1, locked for C1
9d. Killer pair 3,5 in 20(3) cage and R6C2 for N4, locked for N4, clean-up: no 6 in R7C3 (step 6)
9e. Min R34C3 = 9 -> max R4C4 = 5 (because 15(3) cage cannot be [366])
9f. Min R4C34 = 7 -> max R3C3 = 8, clean-up: no 2 in R3C6 (step 5)

10. 19(4) cage at R6C1 = {1369/1378/1567/2359/2368} (cannot be {1279} because R6C2 only contains 3,5)
10a. Killer pair 1,2 in R45C1 and R78C1, locked for C1

11. 1,2 in N1 locked in 9(3) cage = {126}, locked for N1, clean-up: no 5 in R3C6 (step 5)
11a. Naked triple {126} in R234C2, locked for C2
11b. 6 in C2 locked in R23C2, locked for N1

12. R123C1 = {358} (only remaining combination), locked for C1 and N1, clean-up: no 3,6,8 in R3C6 (step 5)
12a. Naked pair {47} in R3C36, locked for R3, clean-up: no 6 in R6C7 (step 4)
12b. R3C3 + R4C4 can only total 8 as [71] -> no 7 in R4C3, clean-up: no 4 in R7C3 (step 6)
12c. 9 in N1 locked in R1C23, locked for R1 and 24(4) cage

13. 6 in C1 locked in R678C1
13a. 19(4) cage at R6C1 (step 10) = {1369/1567}, no 2, 1 locked in R78C1, locked for C1 and N7
13b. Grouped X-Wing for 1 in R78C1 and 8(3) cage in N8, no other 1 in R78
13c. 2 in N7 locked in R789C3, locked for C3 -> R2C3 = 1
13d. R4C2 = 1 (hidden single in C2)

14. Max R3C67 = 13 -> min R4C6 = 4
14a. R34C6 cannot total 14 -> no 3 in R3C7, clean-up: no 7 in R6C7 (step 4)
14b. R3C67 cannot total 12 -> no 5 in R4C6

15. 21(3) cage at R6C6 = {489} (only remaining combination), 4 locked in R6C67, locked for R6

16. 45 rule on N7 3 innies R78C1 + R7C3 = 12 = {129/156} (cannot be {237} because 2,3 only in R7C3), no 3,7, clean-up: no 8 in R4C3 (step 6)

17. 9 locked in 24(4) cage at R1C2 = {2679/3489/3579/4569} (cannot be {1689/2589} because R1C23 must contain two of 4,7,9), no 1
17a. R1C23 must contain two of 4,7,9 -> no 4,7 in R12C4
17b. 1 in N2 locked in R1C56, locked for R1
17c. 11(3) cage = {128/137/146}, no 5

18. 1 in N3 locked in R3C79
18a. R23C9 + R3C7 (step 2) = {128/137/146}, no 5
18b. 4,7 of {137/146} must be in R2C9 -> no 3,6 in R2C9

19. 45 rule on N4 3 innies R4C3 + R6C12 = 18 = {369/567}, 6 locked for N4

20. 9 in N2 locked in 19(3) cage = {289/379/469}, no 5
20a. 5 in N2 locked in R12C4, locked for C4
20b. 24(4) cage at R1C2 (step 17) = {3579/4569}, no 2,8

21. R34C3 cannot total 12 -> R4C4 = 2, R45C1 = [42]
21a. R7C34 cannot total 12 -> R6C4 = 1, R7C34 = 14 = [59], R4C3 = 6 (step 6), R3C3 = 7 (cage sum), R3C6 = 4, R7C7 = 8, R6C67 = [94], R6C1 = 7, R6C2 = 5 (step 19), R9C1 = 9, R9C23 = 9 = [72]
21b. Naked pair {49} in R1C23, locked for R1, R12C4 (step 17) = {56}, locked for C4 and N2
21c. 8 in N7 locked in R8C23, locked for R8

22. 45 rule on N5 1 remaining innie R4C6 = 7, R3C7 = 6 (cage sum), R23C2 = [62], R12C4 = [65]
22a. R3C7 = 6 -> R23C9 (step 2) = [23/41]
22b. R23C9 = 5 -> R4C89 = 14 = {59}, locked for R4 and N6 -> R4C7 = 3, R4C5 = 8
22c. R4C7 = 3 -> R5C78 = 8 = {17}, locked for N6

23. R9C4 = 8 (hidden single in R9), R3C45 = [39], R2C5 = 7 (step 20), R2C7 = 9, R3C9 = 1, R2C9 = 4 (step 22a), R58C4 = [47], R9C5 = 4 (cage sum), clean-up: no 3 in 8(3) cage in N8 (prelim h)
23a. R2C7 = 9 -> R23C8 = 11 = [38], R123C1 = [385], R2C6 = 2, R1C56 = [18], R7C56 = [21], R8C5 = 5, R78C1 = [61], R8C7 = 2
23b. R5C6 = 5 (hidden single in C6)

24. R8C7 = 2 -> R78C8 = 11 = [74]

and the rest is naked singles

Hi all

I have been thinking about which puzzle to post as a V2 for a while. I have 2 fun puzzles and I have finally decided to post this puzzle. I can also post the other one if no-one has a problem with it. I enjoyed solving both puzzles, but decided to post the one that felt more difficult.

Assassin 125V2



SS-Score: 1.62
Estimated Rating: 1.5

PS-Code

Solution

Enjoy

Para

Great Killer, Para! It's quite unusual that you still had to use an advanced move (XY-Wing in former version of my wt) to finish this Assassin even though almost all placements were made.

Edit: Simplified wt. I thought that the Killer was finished so as always I used SimpleSudoku to verify if only (Naked and Hidden) Singles were needed to solve it but it needed more. So I immediately looked for cells with two candidates for chains instead of (technical) easier cage blockers to crack it.

A125 V2 Walkthrough:

1. N1247
a) 24(3) = {789} locked for N2
b) 14(3) = {356} locked for N2
c) Innies N12 = 10(2) = [64/82/91]
d) Innies N4 = 9(3) <> 7,8,9
e) Innies N7 = 10(3) <> 8,9
f) Innies N47 = 3(2) = {12} locked for C3
g) 16(3) @ N1 = {169/178/259/268} <> 3,4 because R4C3 = (12); R4C4 <> 1,2

2. N3689
a) Innies N36 = 6(2) = {15/24}
b) Innies N6 = 10(3) <> 8,9
c) Innies N8 = 10(3) <> 8,9
d) Innies N89 = 14(2) = [59/68]
e) 13(3) = 5{17/26} since R7C3 = (12) and R7C4 = (56) -> 5 locked for C4; R6C4 = (567)
f) Innies N8 = 10(3) = {136/145/235} <> 7 since R7C4 = (56); R89C6 <> 5,6
g) 18(3) @ N6: R6C6 <> 1,2,3 because R67C7 <= 14

3. C456
a) 14(3) = {356} -> 5 locked for C5
b) 12(3): R4C6 <> 1,2 since R3C67 <= 9
c) 12(3) = {129/147/156/246/345} <> 8 because R3C67 = (1245); R4C6 = (3679)

4. N1247
a) Outies N47 = 26(3+1): R3C3 <> 9 since R467C4 >= 18
b) Innies N12 = 10(2) <> 1
c) 1 locked in R12C4 @ N2 for C4+12(4)
d) Innies N1 = 15(3): R1C23 <> 6 since R3C3 = (68)
e) 12(4) = {1245} -> 5 locked for R1+N1
f) 17(3) @ N1 <> 3 because {368} blocked by R3C3 = (68)
g) 3 locked in 13(3) @ N1 = 3{19/28/46} <> 7 -> 3 locked for C1
h) Innies N7 = 10(3) = 1{27/45} -> 1 locked for N7

5. R1+C456 !
a) ! Hidden Killer pair (36) in R1C1 + 15(3) for R1 -> R1C1 = (36) and
15(3) = {168/267/348} <> 9
b) 9 locked in R1C56 @ R1 for N2
c) Innies+Outies C6789: -1 = R1C5 - R57C6 -> R57C6 <= 10 must have one of (1234)
d) ! Killer quad (1234) locked in R389C6 + R57C6 for C6
e) 1,2,3,4 locked in 19(5) @ N5 = {12349} locked for N5
f) 12(3) = 4{17/26} because R3C6 = (24) -> 4 locked for R3
g) 5 locked in R6C46 @ N5 for R6

6. N3689
a) Innies N36 = 6(2) = {24} locked for C7
b) 12(3) = {246} -> R4C6 = 6; 2 locked for R3
c) 18(3) @ N6 = 9{27/45} -> R7C7 = 9
d) Innie N89 = R7C4 = 5
e) R6C4 = 7 -> R7C3 = 1, R4C4 = 8, R3C3 = 6, R4C3 = 2
f) R6C6 = 5 -> R6C7 = 4, R3C7 = 2, R1C1 = 3
g) 15(3) = {168} locked for R1+N3
h) 17(3) = {359} locked for N3; 9 also locked for C8
i) R3C9 = 7, R2C9 = 4, R3C4 = 3, R3C5 = 5, R2C5 = 6, R3C8 = 9

7. N469
a) Innies N4 = 7(2) = {16} locked for R6+N4
b) 17(4) = {1457} -> 1,5 locked for R6+N6
c) 19(3) @ N6 = {289} locked for N6
d) 10(3) = 3{16/25} -> 3 locked for N9
e) 18(3) = 6{48/57} -> 6 locked for N9
f) 10(3) = {235} locked for C9+N9
g) 13(4) = {1237} -> 1,7 locked for R9+N9 and R89C6 = {23} locked for C6+N8

8. N478
a) 19(3) @ N8 = {469} locked for N8
b) 8 locked in 19(3) @ R9 for N7 -> 19(3) = 8{29/56}
c) 3 locked in 16(3) @ N7 = 3{49/67}
d) 17(3) = 5{39/48} -> 5 locked for N4
e) 5 locked in R89C1 @ C1 for N7
f) 19(3) @ N7: R9C1 <> 6 because 5 only possible there
g) Hidden Single: R6C1 = 6 @ C1
h) R6C2 = 1, R3C2 = 8, R3C1 = 1 -> R2C1 = 9, R2C3 = 7, R2C2 = 2
i) Naked triple (469) locked in R9C245 for R9
j) R9C3 = 8

9. R789 !
a) 16(3) @ N8 = {178} -> R8C5 = 1; {78} locked for R7
b) 16(4) = 16{27/45} -> R8C1 = (57)
c) ! 16(3) @ N7: R7C2 <> 6 since {367} blocked by R8C169 = (2357)
d) 16(3) @ N7 = {349} because (67) only possible @ R8C2
-> {349} locked for N7 and 9 also locked for R8

10. Rest is singles.

Rating: 1.25. I used a Killer quad.

My solving path was quite similar to Afmob's, and I had no time to write the walkthrough anyway, but just like to comment that I did his most critical steps (#5 & #10) quite differently, and didn't need any killer pairs/triples/quads, innie-outies or xy-wing.


So in hindsight this is not that worthy as a V2.

Perhaps the other one will be more worthy. Please post it Para!

_________________
ADYFNC HJPLI BVSM GgK Oa m

Thanks Para for a challenging V2. I managed to finish it yesterday but have only gone through Afmob's walkthrough and udosuk's alternative steps today.

This puzzle clearly has a fairly narrow solving path. udosuk commented that his path was similar to Afmob's and so was mine. There are clearly two critical points, one in the middle and the other at the end.

Although they aren't technically difficult the two breakthroughs, whichever way they are done (and I missed the simpler way for the second one), are IMHO difficult to spot so I can't accept udosuk's overall comment; I felt that it was a worthy V2, significantly harder than A125.

I'll rate A125 V2 at 1.5 the way I solved it, because my final breakthrough is a very short chain. However if I'd found the simpler way, step 9c in Afmob's edited walkthrough or as given in udosuk's comments, then it's clearly 1.25.

Here is my walkthrough. When I found the first breakthrough at step 17, I removed a few steps that didn't lead to anything helpful but haven't otherwise tried to optimise it. Thanks Afmob for pointing out a couple of typos and a simpler explanation for step 15.

Prelims

a) 24(3) cage in N2 = {789}, locked for N2
b) 19(3) cage in N4 = {289/379/469/478/568}, no 1
c) 19(3) cage in N6 = {289/379/469/478/568}, no 1
d) R9C123 = {289/379/469/478/568}, no 1
e) 19(3) cage in N8 = {289/379/469/478/568}, no 1
f) R789C9 = {127/136/145/235}, no 8,9
g) 12(4) cage at R1C2 = {1236/1245}, no 7,8,9
h) 13(4) cage at R8C6 = {1237/1246/1345}, no 8,9
i) 19(5) cage in N5 must contain 1, locked for N5

1. 45 rule on N2 3 innies R12C4 + R3C6 = 7 = {124}, locked for N2

2. 45 rule on N47 2 innies R47C3 = 3 = {12}, locked for C3
2a. Max R4C3 = 2 -> min R3C3 + R4C4 = 14, no 2,3,4

3. 45 rule on N12 2 innies R3C36 = 10 = [64/82/91], no 5,7

4. 45 rule on N36 2 innies R36C7 = 6 = {15/24}

5. 45 rule on N89 2 innies R7C47 = 14 = {59/68}

6. 45 rule on N4 3 innies R4C3 + R6C12 = 9 = {126/135/234}, no 7,8,9

7. 45 rule on N6 3 innies R4C89 + R6C7 = 10 = {127/136/145/235}, no 8,9

8. 45 rule on N7 3 innies R78C1 + R7C3 = 10 = {127/136/145/235}, no 8,9

9. 45 rule on N9 1 innie R7C7 = 2 outies R89C6 + 4
9a. Min R89C6 = 3 -> no 5,6 in R7C7, clean-up: no 8,9 in R7C4 (step 5)
9b. Max R89C6 = 5, no 5,6,7 in R89C6
9c. Max R67C7 = 14 -> min R6C6 = 4

10. 12(3) cage at R3C6 = {129/147/156/246/345} (cannot be {138/237} because 3,7,8 only in R4C6), no 8
10a. 3,6,7,9 only in R4C6 -> R4C6 = {3679}

11. Max R7C34 = 8 -> min R6C4 = 5
11a. Min R7C34 = 6 -> max R6C4 = 7
11b. 13(3) cage at R6C4 = {157/256}, 5 locked in R67C4, locked for C4
11c. 5 in N2 locked in R23C5, locked for C5
11d. 5 in N8 locked in R7C46, locked for R7

12. 3 in C4 locked in R3589C4
12a. 45 rule on C1234 4 innies R3589C4 = 22 = {2389/3469/3478}, no 1
12a. 1 in C4 locked in R12C4, locked for N2 and 12(4) cage at R1C2, clean-up: no 9 in R3C3 (step 3)

13. 45 rule on N1 3 innies R1C23 + R3C3 = 15
13a. 12(4) cage at R1C2 = {1245} (cannot be {1236} because R1C23 + R3C3 cannot be {36}6}, no 3,6, 5 locked in R1C23, locked for R1 and N1
13b. R1C23 + R3C3 = {258/456}

14. R1C789 = {168/267/348} (cannot be {249} which clashes with R1C23), no 9
14a. Hidden killer pair 3,6 in R1C1 and R1C789 -> R1C1 = {36}
14b. 9 in R1 locked in R1C56, locked for N2

15. R1C123 = {139/238/346} (cannot be {148/247} because R1C1 only contains 3,6), no 7, 3 locked for C1 and N1

16. R78C1 + R7C3 (step 7) = {127/145}, no 6, 1 locked for N7
16a. 5 of {145} must be in R8C1 -> no 4 in R8C1

17. 45 rule on C6789 2 innies R57C6 = 1 outie R1C5 + 1
17a. R1C5 = {789} -> R57C6 = 8,9,10 must contain one of 1,2,3,4
17b. Killer quad 1,2,3,4 in R3C6, R57C6 and R89C6, locked for C6
17c. Min R34C6 = 8 -> max R3C7 = 4, clean-up: no 1 in R6C7 (step 4)

18. 45 rule on N5 4 innies R46C46 = 26 = {5678} (only remaining combination), locked for N5, 5 locked in R6C46, locked for R6, clean-up: no 1 in R3C7 (step 4)
18a. Naked pair {24} in R3C67, locked for R3, R4C6 = 6 (cage sum)
18b. Naked pair {24} in R36C7, locked for C7

19. 18(3) cage at R6C6 = {279/459} -> R7C7 = 9, R7C4 = 5 (step 5), R6C46 = [75], R7C3 = 1 (step 11b), R6C7 = 4, R3C67 = [42], R4C34 = [28], R3C3 = 6, R1C1 = 3, R3C45 = [35], R2C5 = 6
19a. Naked pair {12} in R12C4, locked for C4 and 12(4) cage at R1C2
19b. Naked pair {45} in R1C23, locked for R1 and N1
19c. R1C789 (step 14) = {168} (only remaining combination), locked for R1 and N3 -> R12C4 = [21]
19d. Naked pair {79} in R3C89, locked for R3
19e. Naked pair {18} in R3C12, locked for N1
19f. R2C6 = 8 (hidden single in R2)

20. 17(3) cage in N3 = {359} (only remaining combination) -> R3C8 = 9, R2C78 = {35}, locked for R2 -> R23C9 = [47]
20a. R23C9 = [47] = 11 -> R4C89 = 6 = {15}, locked for R4 and N6

21. R4C3 + R6C12 (step 6) = {126} (only remaining combination), R6C12 = {16}, locked for R6 and N4

22. 6 in C4 locked in 19(3) cage = {469}, locked for N8

23. R7C7 = R89C6 + 4 (step 9)
23a. R7C7 = 9 -> R89C6 = 5 = {23}, locked for C6, N8 and 13(4) cage at R8C6 -> R7C56 = [87], R8C5 = 1, R1C56 = [79], R5C6 = 1
23b. R89C6 = {23} -> R9C78 = {17} (prelim h), locked for R9 and N9

24. R789C9 = {235} (only remaining combination), locked for C9 and N9 -> R4C89 = [51], R2C78 = [53]

25. 19(3) cage in N6 = {289} (only remaining combination) -> R6C8 = 2, R56C9 = {89}, locked for C9 and N6 -> R1C9 = 6
25a. R5C5 = 2 (hidden single in R5)

26. 8 in R9 locked in R9C123, locked for N7
26a. R9C123 = {289/568}, no 3,4
26b. 3 in N7 locked in 16(3) cage = {349/367}, no 2,5
26c. 4 in R9 locked in R9C45, locked for N8

27. 19(3) cage in N4 = {379/478}, no 5, 7 locked for N4
27a. 3 of {379} must be in R4C2 -> no 9 in R4C2
27b. 8 of {478} must be in R5C1 -> no 4 in R5C1
27c. 17(3) cage = {359/458}
27d. 8 of {458} must be in R6C3 -> no 8 in R5C23

28. 5 in C1 locked in R89C1, locked for N7
28a. R9C123 (step 26a) = {289/568}
28b. 5 of {568} must be in R9C1 -> no 6 in R9C1

29. R6C1 = 6 (hidden single in C1), R6C2 = 1, R3C12 = [18], R2C1 = 9 (step 15), R2C23 = [27]
29a. 19(3) cage in N4 (step 27) = {478} (only remaining combination) -> R5C1 = 8, R4C12 = {47}, locked for R4 and N4, R4C7 = 3, R46C5 = [93], R5C4 = 4, R56C9 = [98], R6C3 = 9, R9C3 = 8, R9C5 = 4

30. 16(3) cage in N7 (step 26b) = {349/367}
30a. 7,9 only in R8C2 -> R8C2 = {79}

31. R78C1 + R7C3 (step 16) = {127/145}
31a. R78C1 cannot be [45] => R7C2 + R8C3 = [63] -> R7C12 clashes with R7C8
31b. -> R78C1 = [27]

and the rest is naked singles

In case anyone is wondering about the XY-Wing mentioned by Afmob and udosuk, I didn't spot it either and asked Afmob to show it to me.

In the position after my step 30. R7C1, R7C9 and R8C3 form the XY-Wing. R7C9 and/or R8C3 must be 3, CPE no 3 in R7C2 + R8C9. That then gives a hidden single in R7. IMHO quite a tricky XY-Wing because it uses N7 as one arm of the wing.