f
true
xs
f
eq
s
length
xs
length
cons
a
xs
append
xs
cons
a
nil
length
nil
0
length
cons
x
xs
s
length
xs
eq
0
0
true
eq
s
x
0
false
eq
0
s
y
false
eq
s
x
s
y
eq
x
y
append
xs
ys
appendAkk
reverse
xs
ys
appendAkk
nil
ys
ys
appendAkk
cons
x
xs
ys
appendAkk
xs
cons
x
ys
reverse
nil
nil
reverse
cons
x
xs
append
reverse
xs
cons
x
nil
2.2
reverse
cons
x
xs
reverse
xs
f
true
xs
f
eq
s
length
xs
length
cons
a
xs
append
xs
cons
a
nil
f
true
xs
length
cons
a
xs
append
xs
ys
appendAkk
reverse
xs
ys
append
xs
ys
reverse
xs
f
true
xs
eq
s
length
xs
length
cons
a
xs
f
true
xs
append
xs
cons
a
nil
length
cons
x
xs
length
xs
eq
s
x
s
y
eq
x
y
reverse
cons
x
xs
append
reverse
xs
cons
x
nil
f
true
xs
length
xs
appendAkk
cons
x
xs
ys
appendAkk
xs
cons
x
ys
true
f
true
xs
f
eq
s
length
xs
length
cons
a
xs
append
xs
cons
a
nil
true
Failed!
NaTT
certifiable-1.6