b
a
x1
a
a
d
x1
a
c
x1
b
b
x1
d
a
b
x1
b
d
d
c
x1
d
x1
a
x1
b
a
c
a
x1
x1
2.2
a
c
x1
b
x1
b
a
x1
a
a
d
x1
d
x1
a
x1
b
a
x1
a
d
x1
d
a
b
x1
d
c
x1
d
a
b
x1
b
d
d
c
x1
a
c
x1
b
b
x1
b
a
x1
d
x1
d
a
b
x1
d
d
c
x1
true
d
a
b
x1
d
d
c
x1
b
a
x1
d
x1
a
c
x1
b
b
x1
d
a
b
x1
b
d
d
c
x1
d
x1
a
x1
b
a
x1
a
a
d
x1
d
a
b
x1
d
c
x1
b
a
x1
a
d
x1
a
c
x1
b
x1
true
Failed!
NaTT
certifiable-1.6