a__f
X
X
a__f
a
b
a__b
a
mark
f
X1
X2
a__f
mark
X1
X2
mark
b
a__b
mark
a
a
a__f
X1
X2
f
X1
X2
a__b
b
2.2
mark
f
X1
X2
mark
X1
a__f
X
X
a__f
a
b
mark
f
X1
X2
a__f
mark
X1
X2
mark
b
a__b
true
mark
f
X1
X2
mark
X1
true
a
0
0
b
0
0
a__b
0
0
a__f
2
0
a__b
0
0
f
2
1
1
mark
1
1
0
mark
1
0
a__f
2
0
mark
f
X1
X2
a__f
mark
X1
X2
false
a__f
X
X
a__f
a
b
true
Failed!
NaTT
certifiable-1.6