and
true
X
X
and
false
Y
false
if
true
X
Y
X
if
false
X
Y
Y
add
0
X
X
add
s
X
Y
s
add
X
Y
first
0
X
nil
first
s
X
cons
Y
Z
cons
Y
first
X
Z
from
X
cons
X
from
s
X
2.2
from
X
from
s
X
first
s
X
cons
Y
Z
first
X
Z
add
s
X
Y
add
X
Y
true
add
s
X
Y
add
X
Y
true
s
1
1
1
and
2
0
false
0
0
true
0
0
if
3
0
0
0
0
from
1
0
first
2
0
nil
0
0
first
2
0
from
1
0
cons
2
0
if
3
0
add
2
1
0
add
2
0
and
2
0
first
s
X
cons
Y
Z
first
X
Z
true
s
1
1
and
2
0
false
0
0
true
0
0
if
3
0
0
0
0
from
1
0
first
2
2
0
nil
0
0
first
2
0
from
1
0
cons
2
2
1
if
3
0
add
2
0
add
2
0
and
2
0
from
X
from
s
X
true
Failed!
NaTT
certifiable-1.6