f
true
xs
f
isList
xs
append
cons
a
nil
xs
isList
nil
true
isList
cons
x
xs
isList
xs
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
isList
cons
x
xs
isList
xs
reverse
cons
x
xs
append
reverse
xs
cons
x
nil
append
xs
ys
reverse
xs
reverse
cons
x
xs
reverse
xs
f
true
xs
append
cons
a
nil
xs
f
true
xs
f
isList
xs
append
cons
a
nil
xs
appendAkk
cons
x
xs
ys
appendAkk
xs
cons
x
ys
append
xs
ys
appendAkk
reverse
xs
ys
f
true
xs
isList
xs
true
f
true
xs
f
isList
xs
append
cons
a
nil
xs
true
Failed!
NaTT
certifiable-1.6