sum
0
0
sum
s
x
+
sum
x
s
x
sum1
0
0
sum1
s
x
s
+
sum1
x
+
x
x
2.2
sum1
s
x
sum1
x
sum
s
x
sum
x
true
sum
s
x
sum
x
true
s
1
1
1
sum
1
0
0
0
0
sum1
1
0
+
2
0
sum
1
1
0
sum1
1
0
sum1
s
x
sum1
x
true
s
1
1
1
sum
1
0
0
0
0
sum1
1
1
0
+
2
0
sum
1
0
sum1
1
0
NaTT
certifiable-1.6