le
0
y
true
le
s
x
0
false
le
s
x
s
y
le
x
y
app
nil
y
y
app
add
n
x
y
add
n
app
x
y
low
n
nil
nil
low
n
add
m
x
if_low
le
m
n
n
add
m
x
if_low
true
n
add
m
x
add
m
low
n
x
if_low
false
n
add
m
x
low
n
x
high
n
nil
nil
high
n
add
m
x
if_high
le
m
n
n
add
m
x
if_high
true
n
add
m
x
high
n
x
if_high
false
n
add
m
x
add
m
high
n
x
head
add
n
x
n
tail
add
n
x
x
isempty
nil
true
isempty
add
n
x
false
quicksort
x
if_qs
isempty
x
low
head
x
tail
x
head
x
high
head
x
tail
x
if_qs
true
x
n
y
nil
if_qs
false
x
n
y
app
quicksort
x
add
n
quicksort
y
2.2
if_low
false
n
add
m
x
low
n
x
if_qs
false
x
n
y
app
quicksort
x
add
n
quicksort
y
if_low
true
n
add
m
x
low
n
x
low
n
add
m
x
if_low
le
m
n
n
add
m
x
app
add
n
x
y
app
x
y
le
s
x
s
y
le
x
y
quicksort
x
if_qs
isempty
x
low
head
x
tail
x
head
x
high
head
x
tail
x
quicksort
x
high
head
x
tail
x
if_qs
false
x
n
y
quicksort
x
low
n
add
m
x
le
m
n
if_high
true
n
add
m
x
high
n
x
quicksort
x
tail
x
quicksort
x
head
x
quicksort
x
head
x
quicksort
x
head
x
quicksort
x
low
head
x
tail
x
high
n
add
m
x
if_high
le
m
n
n
add
m
x
if_high
false
n
add
m
x
high
n
x
if_qs
false
x
n
y
quicksort
y
quicksort
x
isempty
x
high
n
add
m
x
le
m
n
quicksort
x
tail
x
true
quicksort
x
if_qs
isempty
x
low
head
x
tail
x
head
x
high
head
x
tail
x
if_qs
false
x
n
y
quicksort
y
if_qs
false
x
n
y
quicksort
x
true
Failed!
NaTT
certifiable-1.6