Prelims
a) R2C23 = {79}
b) R2C45 = {49/58/67}, no 1,2,3
c) 11(2) cage at R3C6 = {29/38/47/56}, no 1
d) R45C1 = {19/28/37/46}, no 5
e) 12(2) cage at R5C2 = {39/48/57}, no 1,2,6
f) 9(2) cage at R6C3 = {18/27/36/45}, no 9
g) R6C56 = {16/25/34}, no 7,8,9
h) R89C9 = {59/68}
i) R9C56 = {18/27/36/45}, no 9
j) 6(3) cage at R3C4 = {123}
k) 22(3) cage at R4C5 = {589/679}
l) 19(3) cage at R6C7 = {289/379/469/478/568}, no 1
m) 6(3) cage at R8C5 = {123}
n) 14(4) cage at R1C1 = {1238/1247/1256/1346/2345}, no 9
o) 40(8) cage at R5C3 = {12346789}, no 5
1a. Naked pair {79} in R2C23, locked for R2 and N1, clean-up: no 4,6 in R2C45
1b. Naked pair {58} in R2C45, locked for R2 and N2, clean-up: no 3,6 in R4C7
1c. Naked triple {123} in 6(3) cage at R3C4, locked for C4, clear-up: no 6,7,8 in R6C3
1d. Naked triple {123} in 6(3) cage at R8C5, locked for R8
1e. 22(3) cage at R4C5 = {589/679}, 9 locked for N5
1f. Killer triple 1,2,3 in R45C4 + R6C56, locked for N5
2a. 45 rule on N3 2 outies R12C6 = 8 = [26/62/71]
2b. 45 rule on R6789 2 outies R5C23 = 9 = [36/54/72/81], no 9, no 4 in R5C2, no 3,7,8 in R5C3, clean-up: no 3,8 in R6C3
2c. 45 rule on N1 2 outies R4C23 = 1 innie R1C3 + 8, IOU no 8 in R4C2
2d. 45 rule on C1234 3 outies R127C5 = 19 = {289/478/568} (cannot be {379/469} because R2C5 only contains 5,8), no 1,3, 8 locked for C5, clean-up: no 1 in R9C6
2e. 15(3) cage at R1C3 = {249/456} (cannot be {159/168/258/348/357} because 1,3,5,8 only in R1C3, cannot be {267} which clashes with R1C6), no 1,3,7,8, 4 locked for R3
2f. 5 of {456} must be in R1C3 -> no 6 in R1C3
2g. R12C6 = [62/71] (cannot be [26] which clashes with 15(3) cage)
2h. 3 in N2 only in R3C456, locked for R3
2i. 3 in N1 only in 14(4) cage at R1C1 = {1238/1346} (cannot be {2345} which clashes with R1C3), no 5, 1 locked for N1
3a. 7 in C4 only in R6789C4, CPE no 7 in R7C5
3b. R127C5 (step 2d) = {289/568}, no 4
3c. 6 of {568} must be in R1C5 -> no 6 in R7C5
3d. 22(3) cage at R4C5 = {679} (cannot be {589} which clashes with R127C5, ALS block), locked for N5, clean-up: no 1 in R6C56
3e. 1 in N5 only in R45C4, locked for C4
3f. 8 in N5 only in R4C4 + R6C6, locked for D/
3g. Killer triple 6,7,9 in R127C5 and R45C5, locked for C5, clean-up: no 2,3 in R9C6
3h. Hidden killer triple 6,7,9 in R1C45 and R13C6 for N2, R1C45 contains one of 6,9 (step 2e), R1C6 = {67} -> R3C6 = {679}, R4C7 = {245}
3i. Naked triple {679} in R135C6, locked for C6, clean-up: no 2,3 in R9C5
3j. 6 in N8 only in R789C4, locked for C4
4a. 15(3) cage at R1C3 (step 2e) = {249/456}, R127C5 (step 3b) = {289/568}
4b. R127C5 = {289} (cannot be {568} = [658] because R6C4 = 4 clashes with 15(3) cage = [546]) -> R17C5 = {29}, locked for C5, R2C5 = 8 -> R2C4 = 5, clean-up: no 4 in R6C3, no 5 in R6C6
[Probably clearer as a forcing chain.
Consider placements for R6C6 = {48}
R6C6 = 4 => R1C4 = 9 => 15(3) cage = [492] => R127C5 = [289]
or R6C6 = 8 => R7C5 = {29} => R127C5 = {289}
-> R127C5 = {289} -> R17C5 = {29}, locked for C5, R2C5 = 8 -> R2C4 = 5, clean-up: no 4 in R6C3, no 5 in R6C6]
4c. 15(3) cage = {249} (only remaining combination), locked for R1, 9 locked for N2, clean-up: no 2 in R4C7
4d. Naked pair {67} in R45C5, locked for N5 -> R5C6 = 9, clean-up: no 1 in R4C1
4e. 5 in N1 only in R3C12, locked for R3 and 23(4) cage at R3C2
4f. Killer pair 2,4 in 14(4) cage at R1C1 (step 2i) and R1C3, locked for N1
5a. 3 in R3 only in R3C45, 5 in R3 only in R3C23
5b. 45 rule on R123 5 innies R3C23456 = 24 = {13578/23568}, no 4
[The last key step; fairly straightforward from here]
5c. R1C4 = 4 (hidden single in N2) -> R1C35 = [29], R6C4 = 8, R7C5 = 2, clean-up: no 7 in R5C2 (step 2b), no 5 in R6C1, no 1,5 in R6C3, no 7 in R7C4
5d. 9(2) cage at R6C3 = [36], clean-up: no 7 in R45C1, no 6 in R5C3 (step 2b), no 9 in R6C1, no 4 in R6C56
5e. R6C56 = [52], R4C6 = 4, placed for D/, R4C7 = 5 -> R3C6 = 6, clean-up: no 6 in R5C1
5f. 2 on D/ only in R2C8 + R3C7, locked for N3
5g. 12(3) cage at R2C9 = {138/147}, no 9, 1 locked for N3
5h. R3C7 = 9 (hidden single in N3), placed for D/, R2C6 = 1 -> R1C9 + R2C8 = 7 = [52], clean-up: no 9 in R89C9
[No more clean-ups]
5i. R8C567 = [132], R9C5 = 4 -> R9C6 = 5
5j. R7C6 = 8 -> R67C7 = 11 = {47}, locked for C7
5k. R1C6 = 7, R1C78 + R2C7 = {368}, locked for N3 -> R2C9 = 4, R3C89 = {17}, 1 locked for R3
5l. R3C23 = {58}, 8 locked for N1 and 23(4) cage at R3C2 -> R4C23 = 10 = {19}, locked for R4 and N4
5m. R7C3 + R9C1 = [13] (hidden pair on D/)
5n. R3C1 = 4, R6C1 = 7 -> R5C2 = 5, R5C3 = 4, R6C2 = 6, R8C2 = 7, placed for D/, R5C5 = 6, placed for D\, R2C2 = 9, placed for D\, R9C9 = 8, placed for D\ -> R3C3 = 5, placed for D\
and the rest is naked singles, without using the diagonals.