Thanks Afmob and Ed for the corrections.
Prelims
a) R1C12 = {19/28/37/46}, no 5
b) R67C1 = {15/24}
c) 6(2) cage at R6C4 = {15/24}
d) R6C56 = {29/38/47/56}, no 1
e) R6C78 = {39/48/57}, no 1,2,6
f) R89C9 = {18/27/36/45}, no 9
g) R9C34 = {39/48/57}, no 1,2,6
h) 21(3) cage at R3C1 = {489/579/678}, no 1,2,3
i) 11(3) cage at R8C4 = {128/137/146/236/245}, no 9
j) 40(8) cage at R1C7 = {12346789}, no 5
k) 41(8) cage at R6C3 = {12356789}, no 4
1. 5 in N3 only in R1C89 + R2C79 + R3C8, locked for 36(7) cage at R1C6, no 5 in R1C6 + R4C9
1a. Since the 36(7) cage contains 5 it must also contain 4, 40(8) cage at R1C8 contains 4 -> outies of N3 must contain 4, CPE no 4 in R4C6
1b. Similarly 36(7) cage must contain 9, 40(8) cage contains 9 -> outies of N3 must contain 9, CPE no 9 in R4C6
2. 45 rule on C1 4 innies R1289C1 = 26 = {2789/3689/4679/5678} (cannot be {4589} which clashes with R67C1), no 1, clean-up: no 9 in R1C2
3. R7C4 “sees” all cells in N7 except for R9C3 -> R7C4 = R9C3, no 1,2,6 in R7C4, no 4 in R9C3, clean-up: no 8 in R9C4
3a. 4 in N7 only in R7C13, locked for R7
3b. 4 in R7C13 -> either R67C1 = [24] or 6(2) cage at R6C4 = [24] (locking cages) -> 2 in R6C14, locked for R6, clean-up: no 9 in R6C56
3c. 41(8) cage at R6C3 = {12356789}, 2 locked for N7, clean-up: no 4 in R6C1, no 4 in R6C4
3d. 2 in R6C14, CPE no 2 in R9C1 using D/
3e. 6 in N7 only in R7C2 + R8C123 + R9C12, locked for 41(8) cage, no 6 in R6C3
4. R6C3 “sees” all cells in N7 except for R7C1 -> R6C3 = R7C1 = {15}
4a. R7C3 = 4 (hidden single in R7) -> R6C4 = 2, both placed for D/
4b. Naked pair {15} in R67C1, locked for C1
4c. Naked pair {15} in R6C13, locked for R6 and N4, clean-up: no 6 in R6C56, no 7 in R6C78
5. R6C56 = {47} (cannot be {38} which clashes with R6C78), locked for R6 and N5, clean-up: no 8 in R6C78
5a. Naked pair {39} in R6C78, locked for R6 and N6
6. 18(3) cage at R5C2 = {369/378/468} (cannot be {279} because R6C2 only contains 6,8), no 2
6a. 2 in N4 only in R45C1, locked for C1, clean-up: no 8 in R1C2
6b. 13(3) cage at R3C1 contains 2 = {238/247}, no 6,9
7. 21(3) cage at R3C2 = {489/579} (cannot be {678} which clashes with R6C2), no 6
7a. 21(3) cage = {489/579}, CPE no 9 in R5C2
8. 45 rule on N4, using R6C13 = {15} = 6, 2 outies R3C12 = 13 = [49/85]
8a. 13(3) cage at R3C1 (step 6b) = {238/247}
8b. R3C1 = {48} -> no 4,8 in R45C1
8c. 4 in N4 only in R45C2, locked for C2, clean-up: no 6 in R1C1
9. 6 in N4 only in 18(3) cage at R5C2 (step 6) = {369/468}, no 7
9a. 3 of {369} must be in R5C2, 4 of {468} must be in R5C2 -> R5C2 = {34}
9b. R5C2 = {34} -> no 3 in R5C3
10. 21(3) cage at R3C2 = {489/579}
10a. 4 of {489} must be in R4C2 -> no 8 in R4C2
11. 45 rule on N78 2 outies R6C13 = 1 innie R8C6, R6C13 = {15} = 6 -> R8C6 = 6, clean-up: no 3 in R9C9
11a. R8C6 = 6 -> R89C7 = 11 = {29/38/47}, no 1,5
12. 45 rule on N9 2 remaining innies R7C89 = 11 = {29/38/56}, no 1,7
13. 45 rule on N1, using R3C12 = 13, 2 remaining innies R12C3 = 7 = {16/25}, no 3,7,8,9
13a. Killer pair 1,5 in R12C3 and R6C3, locked for C3, clean-up: no 5 in R7C4 (step 3), no 7 in R9C4
13b. R12C3 = 7 -> R1C45 = 9 = {18/36/45}/[72], no 9 in R1C4, no 7,9 in R1C5
14. 15(3) cage at R2C1 = {168/249/258/357} (cannot be {159/267/456} which clash with R12C3, cannot be {348} which clashes with R3C1
14a. 4 of {249} must be in R2C1 -> no 9 in R2C1
14b. 1,5 of {168/258/357} must be in R2C2 -> no 3,6,7,8 in R2C2
14c. 15(3) cage = {168/249/258/357}, R12C3 (step 13) = {16/25} -> combined cage = {168}{25}/{249}{16}/{258}{16}/{357}/{16}, 1,6 locked for N1, clean-up: no 4,9 in R1C1
14d. R1C45 (step 13b) = {18/36/45} (cannot be [72] which clashes with R1C12), no 7 in R1C4, no 2 in R1C5
15. 9 in C1 only in R89C1, locked for N7 and 41(8) cage at R6C3, no 9 in R7C4 (step 3), clean-up: no 3 in R9C4
16. R1289C1 (step 2) = {3689/4679}
16a. 7 of {4679} must be in R1C1 -> no 7 in R289C1
17. 15(3) cage at R2C1 (step 14) = {168/249/258/357}
17a. 3 of {357} must be in R2C1 -> no 3 in R3C3
17b. 3 in C3 only in R89C3, locked for N7
17c. 3 in 41(8) cage at R6C3 only in R7C4 + R8C3, CPE no 3 in R8C45
18. 45 rule on N6 4 innies R4C7 + R456C9 = 19 = {1468/1567/2458/2467}
18a. 5 of {2458} must be in R5C9, 2 of {2467} must be in R4C79 (R4C79 cannot be {47} which clashes with 21(3) cage at R3C2) -> no 2 in R5C9
19. 16(4) cage at R1C3 = {16}{45}/{25}{18} (cannot be {25}{36} which clashes with R1C12), no 3,6 in R1C45
20. 36(7) cage at R1C6 must contain 9 in R1C689 + R2C79 + R3C8, CPE no 9 in R1C7
20a. 9 in R1 only in R1C689, locked for 36(7) cage, no 9 in R2C79 + R3C8
[It took me a long time to find …]
21. 15(3) cage at R2C1 (step 14) = {168/249/258/357}
21a. 6 of {168} must be in R3C3 (15(3) cage cannot be [618] which clashes with 21(3) cage at R3C2 = [948], because 9 in N1 only in R2C2 + R3C23), no 6 in R2C1
21b. 8 of {168/258} must be in R2C1 -> no 8 in R3C3
22. R9C1 = 6 (hidden single in C1), placed for D/, clean-up: no 3 in R8C9
22a. R8C1 = 9 (hidden single in C1), clean-up: no 2 in R9C7 (step 11a)
[Up to this stage I’ve been sticking to Ed’s comment that nothing harder than killer pairs was needed after the initial push. Now I tried some harder steps, but then realised that I’d missed a hidden single, so I’ve re-worked from here.]
23. R6C2 = 6 (hidden single in C2), R6C9 = 8, clean-up: no 3 in R7C8 (step 12), no 1 in R89C9
23a. R89C7 (step 11a) = [29/38/83] (cannot be {47} which clashes with R89C9), no 4,7
23b. Killer pair 3,9 in R6C7 and R89C7, locked for C7
23c. 1 in N9 only in 14(3) cage at R7C7
23d. Hidden killer pair 4,7 in 14(3) cage and R89C9 for N9, R89C9 contains one of 4,7 -> 14(3) cage must contain one of 4,7 = {149/167}, no 2,3,5,8
23e. 9 of {149} must be in R9C8 -> no 4 in R9C8
23f. 6 of {167} must be in R7C7 -> no 7 in R7C7
24. 14(3) cage at R4C8 = {167/257}, no 4, 7 locked for N6
25. 8 in N4 only in R45C3, locked for C3, clean-up: no 8 in R7C4 (step 3), no 4 in R9C4
26. Moved to step 29c. I’d put this step in the wrong place when doing the re-work.
[And now I’ll use one of my harder steps …]
27. Outies of N3 must contain 4 (step 1a) -> 4 in R13C6 + R4C79
27a. Consider placements for 4 in R13C6 + R4C79
4 in R13C6
or 4 in R4C79 => 21(3) cage at R3C2 = 5{79} => R12C3 (step 13) = {16} => R1C45 (step 13b) = {45}
-> 4 in R1C45 + R13C6, locked for N2
28. 12(3) cage at R2C5 = {129/138/237} (cannot be {156} which clashes with R1C45), no 5,6
29. R4C5 = 6 (hidden single in C5)
29a. 6 in N3 only in 36(7) cage at R1C6
29b. Since the 36(7) cage contains 6 it must also contain 3, 40(8) cage at R1C8 contains 3 -> outies of N3 must contain 3, locked for C6
29c. Outies of N3 must contain 9 (step 1b), 9 locked for C6
30. 45 rule on N7, using R6C13 = {15} = 6, 2 remaining outies R79C4 = 12 = [39/75]
30a. 16(3) cage at R7C5 = {178/259/457} (cannot be {349} because 3,9 only in R7C5, cannot be {358} which clashes with R79C4), no 3
30b. R79C4 = [39] (cannot be [75] which clashes with 16(3) cage), R9C3 = 3, R9C7 = 8 -> R8C7 = 3 (cage sum), R6C78 = [93]
31. R4C1 = 3 (hidden single in R4), R5C1 = 2 (hidden single in C1), R3C1 = 8 (cage sum), R5C2 = 4, R5C3 = 8 (cage sum)
31a. Naked pair {79} in R4C23, locked for R4 and 21(3) cage at R3C2 -> R3C2 = 5, clean-up: no 2 in R12C3 (step 13)
32. R1C1 = 7, placed for D\, R6C6 = 4, placed for D\, R8C8 = 1, placed for D\, R7C7 = 6, placed for D\, R9C8 = 7
32a. R8C9 = 4 (hidden single in N9) -> R9C9 = 5, placed for D\
33. R5C5 = 3 (hidden single on D\), placed for D/, R5C6 = 9 (hidden single in R5), R2C8 = 8, placed for D/, R8C2 = 7, placed for D/, R3C7 = 1, placed for D/, R4C6 = 5
and the rest is naked singles, without using the diagonals.