empty
nil
true
empty
cons
x
l
false
head
cons
x
l
x
tail
nil
nil
tail
cons
x
l
l
rev
nil
nil
rev
cons
x
l
cons
rev1
x
l
rev2
x
l
last
x
l
if
empty
l
x
l
if
true
x
l
x
if
false
x
l
last
head
l
tail
l
rev2
x
nil
nil
rev2
x
cons
y
l
rev
cons
x
rev2
y
l
2.2
rev2
x
cons
y
l
rev2
y
l
if
false
x
l
tail
l
last
x
l
if
empty
l
x
l
if
false
x
l
head
l
rev
cons
x
l
rev2
x
l
rev2
x
cons
y
l
rev
cons
x
rev2
y
l
last
x
l
empty
l
if
false
x
l
last
head
l
tail
l
true
if
false
x
l
last
head
l
tail
l
last
x
l
if
empty
l
x
l
true
Failed!
NaTT
certifiable-1.6