f
i
r
s
t
r
o
w
c
o
n
f
i
g
u
r
a
t
i
o
n
:
2
0
r
e
v
e
r
s
i
b
l
e
-
r
u
l
e
p
a
i
r
1
f
o
r
w
a
r
d
:
r
=
3
2
,
r
u
l
e
=
3
8
5
5
b
a
c
k
w
a
r
d
:
r
=
3
2
,
r
u
l
e
=
2
1
8
4
5