isEmpty
cons
x
xs
false
isEmpty
nil
true
isZero
0
true
isZero
s
x
false
head
cons
x
xs
x
tail
cons
x
xs
xs
tail
nil
nil
p
s
s
x
s
p
s
x
p
s
0
0
p
0
0
inc
s
x
s
inc
x
inc
0
s
0
sumList
xs
y
if
isEmpty
xs
isZero
head
xs
y
tail
xs
cons
p
head
xs
tail
xs
inc
y
if
true
b
y
xs
ys
x
y
if
false
true
y
xs
ys
x
sumList
xs
y
if
false
false
y
xs
ys
x
sumList
ys
x
sum
xs
sumList
xs
0
2.2
sumList
xs
y
isEmpty
xs
sumList
xs
y
p
head
xs
p
s
s
x
p
s
x
sumList
xs
y
inc
y
sum
xs
sumList
xs
0
if
false
false
y
xs
ys
x
sumList
ys
x
if
false
true
y
xs
ys
x
sumList
xs
y
sumList
xs
y
head
xs
inc
s
x
inc
x
sumList
xs
y
tail
xs
sumList
xs
y
isZero
head
xs
sumList
xs
y
if
isEmpty
xs
isZero
head
xs
y
tail
xs
cons
p
head
xs
tail
xs
inc
y
sumList
xs
y
tail
xs
sumList
xs
y
head
xs
true
sum
xs
sumList
xs
0
false
if
false
true
y
xs
ys
x
sumList
xs
y
if
false
false
y
xs
ys
x
sumList
ys
x
sumList
xs
y
if
isEmpty
xs
isZero
head
xs
y
tail
xs
cons
p
head
xs
tail
xs
inc
y
true
Failed!
NaTT
certifiable-1.6