times
x
y
sum
generate
x
y
generate
x
y
gen
x
y
0
gen
x
y
z
if
ge
z
x
x
y
z
if
true
x
y
z
nil
if
false
x
y
z
cons
y
gen
x
y
s
z
sum
xs
sum2
xs
0
sum2
xs
y
ifsum
isNil
xs
isZero
head
xs
xs
y
ifsum
true
b
xs
y
y
ifsum
false
b
xs
y
ifsum2
b
xs
y
ifsum2
true
xs
y
sum2
tail
xs
y
ifsum2
false
xs
y
sum2
cons
p
head
xs
tail
xs
s
y
isNil
nil
true
isNil
cons
x
xs
false
tail
nil
nil
tail
cons
x
xs
xs
head
cons
x
xs
x
head
nil
error
isZero
0
true
isZero
s
0
false
isZero
s
s
x
isZero
s
x
p
0
s
s
0
p
s
0
0
p
s
s
x
s
p
s
x
ge
x
0
true
ge
0
s
y
false
ge
s
x
s
y
ge
x
y
a
c
a
d
2.2
sum
xs
sum2
xs
0
ifsum2
false
xs
y
head
xs
sum2
xs
y
head
xs
isZero
s
s
x
isZero
s
x
sum2
xs
y
isNil
xs
sum2
xs
y
isZero
head
xs
ifsum2
true
xs
y
sum2
tail
xs
y
times
x
y
sum
generate
x
y
ifsum2
false
xs
y
tail
xs
sum2
xs
y
ifsum
isNil
xs
isZero
head
xs
xs
y
ifsum2
false
xs
y
p
head
xs
ge
s
x
s
y
ge
x
y
gen
x
y
z
ge
z
x
times
x
y
generate
x
y
if
false
x
y
z
gen
x
y
s
z
ifsum
false
b
xs
y
ifsum2
b
xs
y
generate
x
y
gen
x
y
0
p
s
s
x
p
s
x
ifsum2
true
xs
y
tail
xs
ifsum2
false
xs
y
sum2
cons
p
head
xs
tail
xs
s
y
gen
x
y
z
if
ge
z
x
x
y
z
true
times
x
y
generate
x
y
false
generate
x
y
gen
x
y
0
false
gen
x
y
z
if
ge
z
x
x
y
z
if
false
x
y
z
gen
x
y
s
z
true
Failed!
NaTT
certifiable-1.6