Prelims
a) R12C1 = {14/23}
b) R12C2 = {39/48/57}, no 1,2,6
c) R12C6 = {49/58/67}, no 1,2,3
d) R45C7 = {14/23}
e) R78C5 = {39/48/57}, no 1,2,6
f) R8C89 = {16/25/34}, no 7,8,9
g) R9C34 = {49/58/67}, no 1,2,3
h) R9C89 = {17/26/34}, no 4,8,9
i) 9(3) cage at R5C2 = {126/135/234}, no 7,8,9
j) 8(3) cage at R7C4 = {125/134}
k) 14(4) cage at R2C6 = {1238/1247/1256/1346/2345}, no 9
l) 26(4) cage at R8C7 = {2789/3689/4589/4679/5678}, no 1
m) 43(8) cage at R1C7 = {13456789}, no 2
Steps resulting from Prelims
1a. 2 in N3 only in R2C8 + R3C78, locked for 17(4) cage at R2C8, no 2 in R4C6
1b. 8(3) cage at R7C4 = {125/134}, CPE no 1 in R8C6
2. 45 rule on N14 2 innies R6C12 = 11 = {29/38/47/56}, no 1
3. 45 rule on N89 2 outies R89C3 = 8 = [17/26/35] -> R9C34 = [58/67/76]
4. 45 rule on N356 1 innie R6C4 = 6, clean-up: no 5 in R6C12 (step 2), no 7 in R9C3, no 1 in R8C3 (step 3)
4a. R6C4 = 6 -> R7C23 + R8C2 = 19 = {289/379/478}, no 1,5
5. 8(3) cage at R7C4 = {125/134}, 1 locked for C4 and N8
5a. R8C3 = {23} -> no 2,3 in R78C4
6. 9(3) cage at R5C2 = {126/135} (cannot be {234} which clashes with R6C12), no 4, 1 locked for N4
7. 45 rule on N5 2 outies R6C78 = 1 remaining innie R4C6 + 11
7a. Max R6C78 = 17 -> no 7,8,9 in R4C6
7b. Min R6C78 = 12, no 1,2 in R6C78
8. 45 rule on N3 3 outies R4C689 = 15, 17(4) cage at R2C8 contains 2 = 2 + 15(3) with overlap at R4C6. Also, because the only other cage in N3 is 43(8) cage at R1C7, the other two values in R2C8 + R3C78 must be in R4C89 -> no 2 in R3C7 (because R23C8 would clash with R4C89)
8a. 2 in N3 only in R23C8, locked for C8, clean-up: no 5 in R8C9, no 6 in R9C9
9. Hidden killer quad 4,7,8,9 in 28(5) cage at R1C3 and R7C3 for C3, 28(5) cage cannot contain all of 4,7,8,9 -> R7C3 = {4789}, R1234C3 must contain three of 4,7,8,9
9a. 28(5) cage at R1C3 = {13789/14689/24589/24679/34579/34678} (cannot be {15679/23689/25678} which only contain two of 4,7,8,9)
9b. Three of 4,7,8,9 must be in R1234C3 -> no 4,7,8,9 in R4C2
10. 45 rule on N5 4 innies R45C6 + R6C56 = 15 = {1239/1248/1257/1347}, 1 locked for N5
11. 9(3) cage at R5C2 = {126/135}, R89C3 = [26/35] -> combined cage 9(3) + R89C3 = {126}[35]/{135}[26], CPE no 2,3,5,6 in R4C3
12. R9C34 = [58/67], R9C89 = [17/26/35] -> combined cage R9C3489 = [58][17]/[58][26]/[67][35], 5 locked for R9
13. 26(4) cage at R8C7 = {2789/3689/4589/4679} (cannot be {5678} which clashes with R9C4)
13a. 26(4) cage = {2789/3689/4589} (cannot be {4679} which clashes with R9C3489)
13b. 7 of {2789} must be in R8C7, 8 of {3689} must be in R8C7 (other permutations clash with R9C3489), 5 of {4589} must be in R8C7 -> R8C7 = {578}
13c. 26(4) cage = {2789/3689/4589} = 7{289}/8{369}/5{489}, 9 locked for R9
13d. Killer pair 6,8 in R9C34 and 26(4) cage, locked for R9, clean-up: no 2 in R9C9
13e. Killer pair 5,7 in R9C34 and R9C89, locked for R9
14. R8C89 = {16/34}/[52], R9C89 = {17/35} -> combined cage R89C89 = {16}{35}/{34}{17}/[52]{17}, 1 locked for N9
15. R7C23 + R8C2 (step 4a) = {289/379/478}
15a. Killer quad 1,2,3,4 in R7C23 + R8C2, R8C3 and R9C12, locked for N7
16. 1 in N7 only in R9C12, locked for R9, clean-up: no 7 in R9C89
16a. Naked pair {35} in R9C89, locked for R9 and N9 -> R9C3 = 6, R9C4 = 7, R8C3 = 2 (step 3), R78C4 = 6 = {15}, locked for C4 and N8, clean-up: no 4 in R8C89
16b. Naked pair {16} in R8C89, locked for R8 and N9 -> R78C4 = [15]
16c. Naked pair {14} in R9C12, locked for R9 and N7
16d. Naked triple {289} in R9C567, locked for 26(4) cage at R8C7 -> R8C7 = 7
17. 3 in N7 only in 25(4) cage at R6C4 = {3679} (only remaining combination), 7,9 locked for N7, 3 locked for C2 -> R78C1 = [58], clean-up: no 9 in R12C2, no 4 in R7C5
18. 9(3) cage at R5C2 (step 6) = {135} (only remaining combination, cannot be {126} because 2,6 only in R5C2), locked for N4, 3 also locked for C3
19. R4C3 = 8 (hidden single in N4)
19a. R7C6 = 6 (hidden single in N8), clean-up: no 7 in R12C6
20. 4 in N9 only in R7C789, locked for 24(5) cage at R7C6, no 4 in R8C6
20a. R78C5 = [84] (cannot be {39} which clashes with R8C6)
[With hindsight, this is better as R8C5 = 4 (hidden single in N8), R7C5 = 8.]
20b. Naked triple {249} in R7C789, locked for R7, N9 and 24(5) cage at R7C3 -> R7C23 = [37], R8C2 = 9, R8C6 = 3, R9C7 = 8
[Overlooked at step 16c]
21. Naked pair {14} in R9C12, locked for 29(6) cage at R6C1, clean-up: no 7 in R6C12 (step 2)
21a. R6C12 = [92], R4C2 = 6
21b. Naked pair {47} in R45C1, locked for C1 and 25(4) cage at R3C1, no 4,7 in R3C12
21c. R9C12 = [14]
21d. R3C1 = 6 (hidden single in C1), R45C1 = {47} = 11 -> R3C2 = 8 (cage sum)
21e. Naked pair {57} in R12C2, locked for C2 and N1 -> R5C2 = 1, clean-up: no 4 in R4C7
22. R6C78 = R4C6 + 11 (step 7)
22a. Max R6C78 = 13 -> R4C6 = 1, R6C78 = 12 = [48/57], clean-up: no 4 in R5C7
22b. Naked pair {23} in R45C7, locked for C7 and N6
23. R4C689 = 15 (step 8) = {159} (only remaining combination), 5,9 locked for R4, N6 and 43(8) cage at R1C7 -> R6C7 = 4, R6C8 = 8 (step 22a), R7C7 = 9, R7C89 = [42], R3C7 = 5
24. R6C9 = 1 (hidden single in N6), R8C89 = [16], R5C89 = [67], R45C1 = [74]
25. R23C8 = {29} (hidden pair in N3), locked for C8 -> R4C89 = [59], R9C89 = [35], R1C8 = 7, R12C2 = [57], clean-up: no 8 in R2C6
26. R4C4 = 4 (hidden single in N5), R4C5 + R5C45 = 20 = {389} (only remaining combination) -> R4C5 = 3, R5C45 = [89], R45C7 = [23], R56C3 = [53], R5C6 = 2, R9C56 = [29], clean-up: no 4 in R12C6
26a, R12C6 = [85], R6C56 = [57], R3C6 = 4, R3C9 = 3, R3C4 = 2, R3C8 = 9, R3C3 = 1, R3C5 = 7, R2C5 = 1 (cage sum)
and the rest is naked singles.