length
nil
0
length
cons
x
l
s
length
l
lt
x
0
false
lt
0
s
y
true
lt
s
x
s
y
lt
x
y
head
cons
x
l
x
head
nil
undefined
tail
nil
nil
tail
cons
x
l
l
reverse
l
rev
0
l
nil
l
rev
x
l
accu
orig
if
lt
x
length
orig
x
l
accu
orig
if
true
x
l
accu
orig
rev
s
x
tail
l
cons
head
l
accu
orig
if
false
x
l
accu
orig
accu
2.2
rev
x
l
accu
orig
if
lt
x
length
orig
x
l
accu
orig
if
true
x
l
accu
orig
tail
l
lt
s
x
s
y
lt
x
y
if
true
x
l
accu
orig
head
l
if
true
x
l
accu
orig
rev
s
x
tail
l
cons
head
l
accu
orig
rev
x
l
accu
orig
lt
x
length
orig
length
cons
x
l
length
l
reverse
l
rev
0
l
nil
l
rev
x
l
accu
orig
length
orig
true
reverse
l
rev
0
l
nil
l
false
if
true
x
l
accu
orig
rev
s
x
tail
l
cons
head
l
accu
orig
rev
x
l
accu
orig
if
lt
x
length
orig
x
l
accu
orig
true
Failed!
NaTT
certifiable-1.6