+
x
0
x
+
0
x
x
+
s
x
s
y
s
s
+
x
y
*
x
0
0
*
0
x
0
*
s
x
s
y
s
+
*
x
y
+
x
y
sum
nil
0
sum
cons
x
l
+
x
sum
l
prod
nil
s
0
prod
cons
x
l
*
x
prod
l
2.2
*
s
x
s
y
*
x
y
+
s
x
s
y
+
x
y
sum
cons
x
l
+
x
sum
l
prod
cons
x
l
prod
l
*
s
x
s
y
+
x
y
*
s
x
s
y
+
*
x
y
+
x
y
sum
cons
x
l
sum
l
prod
cons
x
l
*
x
prod
l
true
sum
cons
x
l
sum
l
true
prod
1
0
s
1
0
prod
1
0
*
2
0
sum
1
0
0
0
0
nil
0
0
cons
2
2
1
+
2
0
sum
1
1
0
+
2
0
*
2
0
prod
cons
x
l
prod
l
true
prod
1
0
s
1
0
prod
1
1
0
*
2
0
sum
1
0
0
0
0
nil
0
0
cons
2
2
1
+
2
0
sum
1
0
+
2
0
*
2
0
prod
cons
x
l
*
x
prod
l
false
sum
cons
x
l
+
x
sum
l
false
*
s
x
s
y
*
x
y
true
prod
1
0
s
1
1
1
prod
1
0
*
2
2
0
sum
1
0
0
0
0
nil
0
0
cons
2
1
+
2
0
sum
1
0
+
2
0
*
2
0
*
s
x
s
y
+
*
x
y
+
x
y
false
*
s
x
s
y
+
x
y
false
+
s
x
s
y
+
x
y
true
prod
1
0
s
1
1
1
prod
1
0
*
2
0
sum
1
0
0
0
0
nil
0
0
cons
2
1
+
2
0
sum
1
0
+
2
2
0
*
2
0
NaTT
certifiable-1.6