Thanks manu for another fun puzzle in this series.
Afmob wrote:
... though some moves might be hard to spot.
Yes some were hard to spot. I got stuck for a while until I found step 10.
I'll rate JFFK5 at Easy 1.5 the way I solved it because I used a very short forcing chain. Technically that's higher rated than innie-outie differences although at a human solving level I don't think it's any harder than Afmob's step 1k.
Here is my walkthrough
Prelims
a) R1C1 + R2C2 = {19/28/37/46}, no 5
b) R1C2 + R2C1 = {14/23}
c) R1C34 = {15/24}
d) R1C67 = {29/38/47/56}, no 1
e) R1C5 + R2C4 = {13}, locked for N2, clean-up: no 5 in R1C3, no 8 in R1C7
f) R1C8 + R2C9 = {29/38/47/56}, no 1
g) R2C6 + R3C5 = {59/68}
h) R3C3 + R4C4 = {39/48/57}, no 1,2,6
i) R34C9 = {16/25/34}, no 7,8,9
j) R4C2 + R5C1 = {15/24}
k) R4C8 + R5C7 = {39/48/57}, no 1,2,6
l) R5C3 + R6C2 = {14/23}
m) R5C9 + R6C8 = {15/24}
n) R67C1 = {29/38/47/56}, no 1
o) R6C6 + R7C7 = {29/38/47/56}, no 1
p) R7C5 + R8C4 = {29/38/47/56}, no 1
q) R8C1 + R9C2 = {29/38/47/56}, no 1
r) R8C6 + R9C5 = {29/38/47/56}, no 1
s) R8C8 + R9C9 = {15/24}
t) R8C9 + R9C8 = {29/38/47/56}, no 1
u) R9C34 = {39/48/57}, no 1,2,6
v) R9C67 = {17/26/35}, no 4,8,9
w) R34C1 = {89}, locked for C1, clean-up: no 1,2 in R2C2, no 2,3 in R67C1, no 2,3 in R9C2
x) R67C9 = {79}, locked for C9, clean-up: no 2,4 in R1C8, no 2,4 in R9C8
y) 9(3) cage in N5 = {126/135/234}, no 7,8,9
A new record number of Prelims! That's because there's also a record number of 2-cell cages.
1. R5C3 + R6C2 = {23} (cannot be {14} which clashes with R4C2 + R5C1), locked for N4, clean-up: no 4 in R4C2 + R5C1
1a. Naked pair {15} in R4C2 + R5C1, locked for N4, clean-up: no 6 in R7C1
2. Killer quad 1,2,3,4 in R1C1 + R2C2, R1C2 + R2C1 and R1C3, locked for N1, clean-up: no 8,9 in R4C4
3. 45 rule on R12 6(1+5) innies R1C9 + R2C35678 = 43
3a. Max R2C35678 = 35 -> R1C9 = 8, R2C35678 = 35 = {56789}, locked for R2, clean-up: no 1,2,3,4 in R1C1, no 3 in R1C7, no 3,5 in R1C8, no 3 in R9C8
3b. R1C9 = 8 -> R2C8 + R3C7 = 9 = [54/63/72]
[With hindsight 45 rule on R1 4 outies R2C1249 = 1 innie R1C9 + 2 -> R1C9 = 8, R2C1249 = 10 = {1234}, locked for R2 is technically slightly easier than steps 3 and 3a.]
4. Killer pair 6,7 in R1C1 and R67C1, locked for C1, clean-up: no 4,5 in R9C2
4a. Killer pair 3,4 in R1C2 + R2C1 and R2C2, locked for N1, clean-up: no 2 in R1C4
5. 3 in R1 locked in R1C25
R1C2 = 3 => R2C1 = 2 => no 1 in R2C1
R1C5 = 3 => R2C4 = 1 => no 1 in R2C1
-> no 1 in R2C1, clean-up: no 4 in R1C2
5a. 1 in N1 locked in R1C23, locked for R1 -> R1C5 = 3, R2C4 = 1, clean-up: no 2 in R2C1, no 8 in R8C4, no 8 in R8C6
5b. Naked pair {12} in R1C23, locked for R1, clean-up: no 9 in R1C67
5c. 2 in C1 locked in R89C1, locked for N7
6. R1C8 = 9 (hidden single in R1), R2C9 = 2, clean-up: no 7 in R2C8 (step 3b), no 5 in R34C9, no 3 in R5C7, no 4 in R6C8, no 4 in R8C8
7. 1,7 in N3 locked in R12C7 + R3C89
7a. 45 rule on N3 4 innies R12C7 + R3C89 = 17 = {1367/1457}
7b. 6,7 of {1367} must be in R12C7, no 6 in R3C89, clean-up: no 1 in R4C9
8. 45 rule on C9 3 outies R689C8 = 2 innies R12C9 + 1
8a. R12C9 = [82] = 10 -> R689C8 = 11 = {128} (only remaining combination) -> R9C8 = 8, R8C9 = 3, R68C8 = {12}, locked for C8, clean-up: no 4 in R34C9, no 4 in R5C7, no 1 in R5C9, no 3,8 in R6C6, no 8 in R7C5, no 4 in R9C34, no 5 in R9C6, no 1 in R9C9
8b. R34C9 = [16]
9. R9C67 = {17/26} (cannot be [35] which clashes with R9C34), no 3,5
9a. Killer triple 6,7,9 in R9C2, R9C34 and R9C67, locked for R9, clean-up: no 2,4,5 in R8C6
10. 4 in R9 locked in R9C159
10a. 45 rule on R9 4 remaining innies R9C1259 = 17 = {1457/2456} (cannot be {1349} because 1,3,9 only in R9C12), no 3,9, clean-up: no 2 in R8C1
10b. R9C34 = {39} (hidden pair in R9)
11. Killer pair 4,5 in R67C1 and R8C1, locked for C1 -> R5C1 = 1, R4C2 = 5, R2C1 = 3, R1C2 = 2, R1C3 = 1, R1C4 = 5, R2C2 = 4, R1C1 = 6, R6C2 = 3, R5C3 = 2, R9C1 = 2, clean-up: no 9 in R2C6 + R3C5, no 7 in R3C3, no 7 in R5C7, no 5 in R7C1, no 6 in R7C5, no 9 in R8C6, no 6 in R9C67
11a. Naked pair {68} in R2C6 + R3C5, locked for N2
[While checking my walkthrough I spotted there is now
X-Wing for 7 in R1C67 and R9C67, locked for C67
but it’s so near the end I didn’t re-work my steps.]
12. R8C1 = 5 (hidden single in C1), R9C2 = 6
13. R9C1 = 2 -> R7C3 + R8C2 = 11 = [38/47]
13a. R7C2 = 1 (hidden single in C2)
13b. 9 in N7 locked in R89C3, locked for C3, clean-up: no 3 in R4C4
13c. R2C5 = 9 (hidden single in R2), clean-up: no 2 in R8C4
14. R3C5 = 6 (hidden single in R3), R2C6 = 8
14a. Naked pair {45} in R59C5, locked for C5, clean-up: no 6,7 in R8C4
15. 9(3) cage in N5 = {234} (only remaining combination, cannot be {126} because R5C5 only contains 4,5, cannot be {135} because R6C4 only contains,2,4,6), no 1,5,6 -> R5C5 = 4
and the rest is naked singles