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