Numbers are 0 to 9.
The numbers in the grey cells repeat horizontally and vertically and are present in every nonet.
No repeats in any other rows or columns.
Each of the other numbers is missing from one and only one nonet.
Five pairs of unknown numbers are semi-symmetric, with the corresponding cell containing the same number or its partner.
Note that in the steps below locked, placements and killer pairs in R6, R7 and C6 don’t apply for R67C6, as appropriate. However placements and locked for N3 and N6 DO apply for R67C6, as appropriate.
Prelims
a) 13(2) cage at R2C6 = {49/58/67}
b) 12(2) cage at R3C4 = {39/48/57}
c) 0(2) cage at R3C6 = [00]
d) 7(2) cage at R4C3 = {07/16/25/34}
e) 14(2) cage at R4C6 = {59/68}
f) 15(2) cage at R5C2 = {69/78}
g) 10(2) cage at R5C7 = {19/28/37/46}
h) 11(2) cage at R5C10 = {29/38/47/56}
i) 6(2) cage at R7C3 = {06/15/24}
j) 11(2) cage at R7C4 = {29/38/47/56}
k) 13(2) cage at R7C5 = {49/58/67}
l) 15(2) cage at R7C11 = {69/78}
m) 6(2) cage at R8C9 = {06/15/24}
n) 13(2) cage at R9C5 = {49/58/67}
o) 2(2) cage at R10C8 = {02}
p) 7(2) cage at R11C5 = {07/16/25/34}
q) 3(3) cage at R5C4 = {012}
r) 8(3) cage at R6C9 = {017/026/035/125/134}
s) 7(3) cage at R7C1 = {016/025/034/124}
t) 4(3) cage at R7C6 = {013}
u) 9(3) cage at R7C7 = {018/027/036/045/126/135/234}
1a. R3C6 = 0, clean-up: no 7 in R11C5
1b. R4C5 = 0, clean-up: no 7 in R5C3, no 7 in R11C6
1c. 3(3) cage at R5C4 = {012), locked for N2, 0 locked for C4, clean-up: 5,6,7 in R45C3
1d. 7(2) cage at R4C3 = {34}, locked for C3 and N2, clean-up: no 7,8 in R7C4, no 2 in R8C2
1e. 4(3) cage at R7C6 = {013}, locked for N6
1f. 2(2) cage at R10C8 = {02), locked for N8, clean-up: no 5 in 7(2) cage at R11C5
1g. 11(3) cage at R5C5 = {128/137/146/236/245}
1h. 8(3) cage at R6C9 = {035/134} (cannot be {017/026/125} which clash with R6C45, ALS block), 3 locked for N4, clean-up: no 7 in R5C7
1i. Killer triple 0,1,2 in R6C45 and 8(3) cage, locked for R6 and 3(3) cage at R5C4, no 2 in R5C4, clean-up: no 8,9 in R5C7
1j. R6C10 = {345} -> R5C10 = {678}
1k. 9(3) cage at R7C7 = {018/027/036/135/234} (cannot be {045/126} which clash with 6(2) cage at R8C9)
1l. 7(3) cage at R7C1 overlaps with 6(2) cage at R7C3 (combo crossover clash), R7C13 and R7C23 cannot total 6 -> no 1 in R7C12
1m. 7(3) cage = {016/025/034/124}
1n. 1 of {016} must be in R7C3 -> no 6 in R7C3, clean-up: no 0 in R8C2
1o. Apart from possibly being in repeat-number cell R6C6, 4 in R6 only in R6C78910,11, locked for N4
1p. 12(3) cage at R4C9 = {057/129/147/246} (cannot be {048/156} which clash with 8(3) cage at R6C9), no 8
1q. 0 of {057} must be in R5C9 -> no 5 in R5C9
1r. 9 on {129} must be in R6C8 -> no 9 in R45C9
1s. 12(3) cage + 8(3) cage must contain 0, locked for N4
[Time to look at semi-symmetry.]
2a. R45C3 = {34} corresponds with R78C10 = {06/15/24}, 7(2) cage at R11C5 = {16/34} corresponds with 13(2) cage at R2C6 = {49/58/67}, {34} cannot correspond with both {06/15/24} and {49/58/67} -> 7(2) cage at R11C5 = {16}, locked for N8
2b. R3C6 = 0 corresponds with R10C6, R4C5 = 0 corresponds with R9C7, neither of R9C7 and R10C6 contain 0 -> R9C7 and R10C6 must contain the same number = {45789}
2c. 11(3) cage at R5C5 corresponds with 4(3) cage at R7C6 = {013}, no 0 in 11(3) cage -> 0 must correspond with one of {4578} -> R9C7 and R10C6 must contain the same number = {4578} -> 11(3) cage = {128/137/146/245} (cannot be {236})
[I was tempted to try to eliminate more combinations but I don’t think any of them stop 13(2) cage at R2C6 corresponding with 7(2) cage at R11C5 = {16}.]
2d. 0 in 4(3) cage only in R7C6 + R8C7, the corresponding number in 11(3) cage is in R5C5 + R6C6 -> no 7,8 in R5C6
2e. 3(3) cage at R5C4 corresponds with 9(3) cage at R7C7, no 0,4,5,7,8 in R6C5 -> no 0 in R7C7
2f. 13(2) cage at R2C6 = {49/58/67} corresponds with 7(2) cage at R11C5 = {16} -> 1 must correspond with at least 4 but cannot be paired with 6 since 13(2) cage doesn’t contain both of 1,6
2g. 9(3) cage at R7C7 (step 1k) = {018/027/036/135/234}
2h. 7(2) cage at R4C3 = {34} corresponds with 6(2) cage at R8C9 = {06/15/24}
2i. {34} with {06} => 0 corresponds with 4, 3 with 6 => 0 in 3(3) cage must correspond with 4 in 9(3) cage but 3(3) cage cannot then correspond with 9(3) cage = {234} because 3 cannot correspond with 1
or {34} corresponds with {15} => 1 must correspond with at least 4 and then 0 in 3(3) cage would have to correspond with 5 in 9(3) cage but {045} already eliminated from 9(3) cage)
-> 6(2) cage = {24}, locked for C9 and N7
[That’s the hard part done, fairly straightforward from here.]
2j. 7(2) cage at R4C3 = {34} corresponds with 6(2) cage at R8C9 = {24} -> 2 paired with 3
2k. 3(3) cage at R5C4 corresponds with 9(3) cage at R7C7, 3(3) cage contains 2 -> 9(3) cage must contain 3 = {135} (cannot be {036} because 1 cannot be paired with 6), locked for N7
2l. {012} corresponds with {135}, 2 paired with 3 -> 0 paired with 5
2m. 0 in 3(3) cage in R56C4 -> 5 in R78C8, locked for C8 and N7
2n. R3C6 = 0 -> R10C6 = 5, R4C5 = 0 -> R9C7 = 5, clean-up: no 8 in 13(2) cage at R2C6, no 9 in 14(2) cage at R4C6, no 8 in R7C5, no 8 in 13(2) cage at R9C5
2o. Naked pair {68} in 14(2) cage at R4C6, locked for R4 and N3, clean-up: no 4 in R6C7
2p. 11(3) cage at R5C5 corresponds with 4(3) cage at R7C6 = {013), 0 paired with 5, 2 with 3 -> 11(3) cage must be {245}, locked for N3 -> 1 paired with 4, clean-up: no 6,8 in R6C7
2r. R2C5 + R3C4 correspond with 2(2) cage at R10C8 -> R2C5 = {235}, R3C4 = {35}, R3C5 = {79}
2s. 13(2) cage at R2C6 with 7(2) cage at R11C5 = {16}, 1 paired with 4 -> 13(2) cage = {49}, locked for N1, 6 paired with 9 -> 7 paired with 8
2t. R3C5 = 7 -> R3C4 = 5, clean-up: no 6 in R8C3
2u. 14(2) cage at R4C6 = {68} corresponds with 13(2) cage at R9C5 = [67]
2v. 7(2) cage at R11C5 = [16] -> 13(2) cage at R2C6 = [94]
2w. 14(2) cage = [86]
3a. R6C5 = 2 -> R2C5 = 3
3b. R6C5 = 2 -> R7C7 = 3, R5C7 = 1 -> R6C7 = 9, R56C4 = [01], clean-up: no 6 in R5C2, no 8 in R8C3
3c. R2C5 = 3 -> R11C7 = 2, R10C8 = 0, R3C7 = 8
3d. R8C7 = 0 -> R5C5 = 5, clean-up: no 8 in R8C5
3e. 8(3) cage at R6C9 = {035}, 5 locked for R6 and N4, clean-up: no 7 in R5C10
3f. R5C2 = 9 (hidden single in N2) -> R6C1 = 6
3g. 15(2) cage at R5C2 corresponds with 15(2) cage at R7C11 = {69}, locked for N7
3h. No 5 in N2 -> no 0 in N7
3i. 12(3) cage at R4C9 = {147} (only remaining combination) = [174] -> R7C910 = [87]
3j. R5C4 = 0 -> R8C8 = 5, R7C8 = 1, clean-up: no 6 in R7C4
3k. 7(3) cage at R7C1 = {025} (only remaining combination), 2 locked for N5, clean-up: no 9 in 11(2) cage at R7C4
3l. 11(2) cage = [47] -> R6C23 = [78], 13(2) cage at R7C5 = [94], 15(2) cage at R7C11 = [69], R10C57 = [87], clean-up: no 2 in R6C3
3m. R8C9 = 2 -> R5C3 = 3
3n. R4C9 = 1 -> R9C3 = 1, R8C2 = 6 -> R7C3 = 0 -> R6C9 = {05}
3o. R8C2 = 6 -> R5C10 = 6, R6C10 = 5, R6C911 = [03]
3p. R6C11 = 3 -> R7C1 = 2
3q. 8 cannot be missing from both of N4 and N5 -> R5C8 = 8, R8C4 = 8, 2 missing from N4, 3 missing from N5
3r. No 8 in N6 -> no 7 in N3
3s. Naked pair {39} in R410C4, locked for C4 -> R9C48 = [29], R4C48 = [93],
3t. R10C4 = 3 -> R3C8 = 2, R112C6 = 1,4
3u. 6 missing from N1, 9 missing from N8
3v. 1,4 must be the repeated numbers -> R67C6 = [41]