isEmpty
nil
true
isEmpty
cons
x
xs
false
last
cons
x
nil
x
last
cons
x
cons
y
ys
last
cons
y
ys
dropLast
nil
nil
dropLast
cons
x
nil
nil
dropLast
cons
x
cons
y
ys
cons
x
dropLast
cons
y
ys
append
nil
ys
ys
append
cons
x
xs
ys
cons
x
append
xs
ys
reverse
xs
rev
xs
nil
rev
xs
ys
if
isEmpty
xs
dropLast
xs
append
ys
last
xs
ys
if
true
xs
ys
zs
zs
if
false
xs
ys
zs
rev
xs
ys
2.2
append
cons
x
xs
ys
append
xs
ys
rev
xs
ys
append
ys
last
xs
reverse
xs
rev
xs
nil
rev
xs
ys
last
xs
last
cons
x
cons
y
ys
last
cons
y
ys
rev
xs
ys
dropLast
xs
rev
xs
ys
if
isEmpty
xs
dropLast
xs
append
ys
last
xs
ys
if
false
xs
ys
zs
rev
xs
ys
dropLast
cons
x
cons
y
ys
dropLast
cons
y
ys
rev
xs
ys
isEmpty
xs
true
reverse
xs
rev
xs
nil
false
if
false
xs
ys
zs
rev
xs
ys
rev
xs
ys
if
isEmpty
xs
dropLast
xs
append
ys
last
xs
ys
true
Failed!
NaTT
certifiable-1.6