Yes:
AiR
air
aiR
aIr
aIR
Air
AIr
AIR
ari
EaRtH
earth
f7re
f7ri
fer7
fir
fir7
fiter
iar
ira
rai
rererer
ria
WaTeR
water
witer
No:
(empty string)
0
0123456789
1
1o
2
3
4
5
5ire
6
6h
6ire
7
8
9
99
a
aa
abcdefghijklmnopqrstuvwxyz
e
f
f1re
f7r7
f8re
fi
fier
fir4
fir5
FiRe
fire
i
ii
iter
r
ri
xx
xy
Less plausible (I expect these patterns are an artifact of our specific tests, not of the rule itself):
You need at least two letters
You need more than two characters
We could probably gain the most information by proving one of the plausible patterns wrong, but I’ll focus on the ones I marked less plausible because it’s correspondingly more likely I can find a counterexample.
fr7: no
f7: yes
r7: yes
fr: no
fe: no
r: no
R: no
rr: no
1r: no
7r: yes
Koans
Yes:
7r
AiR
air
aiR
aIr
aIR
Air
AIr
AIR
ari
EaRtH
earth
f7
f7re
f7ri
fer7
fir
fir7
fiter
iar
ira
r7
rai
rererer
ria
WaTeR
water
witer
No:
(empty string)
0
0123456789
1
1o
1r
2
3
4
5
5ire
6
6h
6ire
7
8
9
99
a
aa
abcdefghijklmnopqrstuvwxyz
e
f
f1re
f7r7
f8re
fe
fi
fier
fir4
fir5
FiRe
fire
fr
fr7
i
ii
iter
r
r
R
ri
rr
xx
xy
Yes:
7r
AiR
air
aiR
aIr
aIR
Air
AIr
AIR
ari
EaRtH
earth
f7
f7re
f7ri
fer7
fir
fir7
fiter
iar
ira
r7
rai
rererer
ria
WaTeR
water
witer
No:
(empty string)
0
0123456789
1
1o
1r
2
3
4
5
5ire
6
6h
6ire
7
8
9
99
a
aa
abcdefghijklmnopqrstuvwxyz
ar
b
c
d
e
er
f
f1re
f7r7
f8re
fe
fi
fier
fir4
fir5
FiRe
fire
fr
fr7
g
h
i
ii
iter
j
k
l
m
n
r
r
R
ri
rr
rr
tr
wr
xx
xy
Yes:
7r
AiR
air
aiR
aIr
aIR
Air
AIr
AIR
ari
EaRtH
earth
f7
f7re
f7ri
fer7
fir
fir7
fiter
iar
ira
r7
rai
rererer
ria
WaTeR
water
witer
No:
(empty string)
0
0123456789
1
1o
1r
2
3
4
5
5ire
6
6h
6ire
7
8
9
99
a
aa
abcdefghijklmnopqrstuvwxyz
ar
ater
b
c
d
e
er
f
f1re
f7r7
f8re
fe
fi
fier
fir4
fir5
FiRe
fire
fr
fr7
g
h
i
ii
iter
j
k
l
m
n
r
R
ri
rr
tr
waer
wate
watr
wr
wter
xx
xy