2*at + s1 -> s2
s2 -> 2*at + s1
s2 -> 2*s3
2*s3 -> s2
na + s3 -> at + s4
at + s4 -> na + s3
s4 -> at + s5
at + s5 -> s4
s5 -> s6
s6 -> s5
at -> 0
0 -> at
s3 -> na
na -> s3
s6o -> 0
0 -> s6o
s6 -> (1/10)*s6o
(1/10)*s6o -> s6
s6 -> na
na -> s6
0 -> s1
s1 -> 0