Prelims
a) R1C45 = {79}
b) R45C9 = {59/68}
c) R56C1 = {12}
d) R9C56 = {29/38/47/56}, no 1
e) 20(3) cage at R1C9 = {389/479/569/578}, no 1,2
f) 11(3) cage at R2C5 = {128/137/146/236/245}, no 9
g) 9(3) cage at R3C4 = {126/135/234}, no 7,8,9
h) 19(3) cage at R5C8 = {289/379/469/478/568}, no 1
i) 11(3) cage at R7C7 = {128/137/146/236/245}, no 9
j) 12(4) cage at R1C2 = {1236/1245}, no 7,8,9
k) 28(4) cage at R2C1 = {4789/5689}, no 1,2,3
Steps Resulting From Prelims
1a. Naked pair {79} in R1C45, locked for R1 and N2
1b. Naked pair {12} in R56C1, locked for C1 and N4
1c. 12(4) cage at R1C2 = {1236/1245}, CPE no 1,2 in R2C2
1d. 28(4) cage at R2C1 = {4789/5689}, CPE no 8 in R1C1
2a. 45 rule on both diagonals R5C5 (repeated) = 4, placed for both diagonals, clean-up: no 7 in R9C6
2b. 45 rule on D\ 2 innies R4C4 + R6C6 = 14 = {59/68}
2c. 45 rule on D/ 2 innies R4C6 + R6C4 = 9 = {18/27/36}, no 5,9
3a. 45 rule on C123 3 outies R259C4 = 10 = {127/136/145/235}, no 8,9
3b. 45 rule on C789 3 outies R158C6 = 22 = {589/679}, 9 locked for C6, clean-up: no 5 in R4C4 (step 2b), no 2 in R9C5
3c. 6 of {679} must be in R1C6 -> no 6 in R58C6
3d. Combined half cage R158C6 + R6C6 = {589}6/{679}{58}, 6 locked for C6, clean-up: no 3 in R6C4 (step 2c), no 5 in R9C5
4a. 45 rule on N1 2 outies R2C4 + R4C1 = 11, no 1 in R2C4, no 4 in R4C1
4b. 12(4) cage at R1C2 = {1236/1245}, 1 locked for N1
4c. 45 rule on N3 2 outies R1C6 + R4C8 = 11 = [56/65/83]
4d. 45 rule on N7 2 outies R7C2 + R9C4 = 11, no 3 in R7C2, no 1 in R9C4
4e. 45 rule on N9 2 outies R6C9 + R8C6 = 11 = [29/38/47/65]
4f. 1 on D\ only in 11(3) cage at R7C7 = {128/137}, no 5,6, 1 locked for N9
4g. R259C4 (step 3a) = {127/136/145/235}
4h. 1 of {127/136} must be in R5C4 -> no 6,7 in R5C4
5a. Min R5C6 = 5 -> max R45C7 = 7, no 7,8,9 in R45C7
5b. 7 in N6 only in 19(3) cage at R5C8 = {379/478}, no 2,5,6
5c. 1 in N6 only in R45C7, locked for C7
5d. 12(3) cage at R4C7 = {129/138/147/156}
5e. 5 of {156} must be in R5C6 -> no 5 in R45C7
5f. 5 in N6 only in R4C8 + R45C9, CPE no 5 in R23C9
6a. R259C4 (step 3a) = {127/136/145/235}, R4C6 + R6C4 (step 2c) = {18/27/36}
6b. Consider combinations for R4C4 + R6C6 (step 2b) = {68}/[95]
R4C4 + R6C6 = {68} => R4C6 + R6C4 = {27} => R259C4 = {136/145/235} (cannot be {127} which clashes with R6C4
or R4C4 + R6C6 = [95], R1C4 = 7
-> R259C4 = {136/145/235}, no 7, clean-up: no 4 in R6C2 (step 4d)
6c. R4C4 + R6C6 = {68}, locked for D\ => 16(3) cage at R1C1 = {259}
or R4C4 + R6C6 = [95], 5,9 placed for D\, R2C4 + R4C1 (step 4a) cannot be [29] => 2 of 12(4) cage in R1C2 + R2C23, locked for N1 => 16(3) cage = {367}
-> 16(3) cage = {259/367}, no 8
[Looking at the other posted walkthroughs I ought to have also spotted 9 in R4C14 from this.]
6d. 8 in N1 only in R2C1 + R3C12, locked for 28(4) cage at R2C1, no 8 in R4C1, clean-up: no 3 in R2C4 (step 4a)
6e. Consider combinations for 16(3) cage = {259/367}
16(3) cage = {259} => 12(4) cage = {136}2, 6 locked for N1
or 16(3) cage = {367}, 6 locked for N1
-> no 6 in R2C1 + R3C12
6f. 28(4) cage at R2C1 = {4789/5689}
6g. 6 of {5689} must be in R4C1 -> no 5 in R4C1, clean-up: no 6 in R2C4 (step 4a)
6h. R259C4 = {145/235} (cannot be {136} because R2C4 only contains 2,4,5), no 6, 5 locked for C4, clean-up: no 5 in R6C2 (step 4d)
6i. 11(3) cage at R2C5 = {128/146/236} (cannot be {245} which clashes with R2C4), no 5
6j. 6 of {236} must be in R2C5 -> no 3 in R2C5
6k. 9(3) cage at R3C4 = {135/234} (cannot be {126} which clashes with 11(3) cage, ALS block), no 6
7a. 45 rule on R123 3 outies R4C158 = 13 = {139/157/256} -> R4C5 = {12}, R4C8 = {35}, clean-up: no 5 in R1C4 (step 4c)
7b. R158C6 (step 3b) = {589/679}
7c. R1C7 = {68} -> no 8 in R58C6, clean-up: no 3 in R6C9 (step 4e)
7d. 12(3) cage at R4C7 (step 5d) = {129/147/156}, no 3
7e. 9(3) cage at R3C4 (step 6k) = {135/234}, 3 locked for R3 and N2
7f. R4C5 = {12} -> no 1,2 in R3C45
7g. R259C4 (step 6h) = {235} (cannot be {145} which clashes with 9(3) cage), locked for C4 -> R3C4 = 4, R34C5 = [32], clean-up: no 7 in R4C1 (step 4a), no 7 in R4C6 + R6C4 (step 2c), no 8 in R9C6
7h. 11(3) cage at R2C5 = {128}, 2,8 locked for N2 -> R1C6 = 6, R58C6 = {79}, 7 locked for C6, clean-up: no 8 in R4C4 (step 2b), no 6 in R6C9 (step 4e)
7i. R2C4 = 5 -> R5C4 = 3, R9C4 = 2 -> R6C2 = 9 (step 4d), R4C1 = 6, clean-up: no 8 in R5C9, no 6 in R6C4 (step 2c), no 9 in R9C5
7j. R2C4 = 5 -> 12(4) cage at R1C2 = {1245}, 2,4 locked for N1 -> 16(3) cage at R1C1 (step 6c) = {367} -> R1C1 = 3, R2C2 + R3C3 = {67}, 3,7 locked for D\, 7 locked for N1
7k. Naked pair {18} in R4C6 + R6C4, locked for N5 and D/
7l. R1C9 = 5 -> R2C8 + R3C7 = 15 = {69}, locked for N3 and D/ -> 12(3) cage at R7C3 = {237}, R9C1 = 7, R7C3 + R8C2 = {23}, locked for N7, clean-up: no 9 in R45C9, no 4 in R9C6
7m. R45C9 = [86] -> R9C9 = 1, R4C6 + R6C4 = [18], R4C4 + R6C6 = [95], R1C45 = [79], R58C6 = [79], R4C7 = 4 -> R5C7 + R6C9 = [12], clean-up: no 6 in R9C5
7n. Naked pair {37} in R6C78, locked for R6 and N6 -> R6C3 = 4, R5C4 = 3 -> R5C3 = 8 (cage sum)
7o. R78C4 = {16} -> R8C5 = 7 (cage sum)
and the rest is naked singles, without using the diagonals.