(SIG
   (a1   -> o)
   (b1   -> o)
   (c1   -> o)
   (b2   -> o)
   (c2   -> o)
   (a2   -> o)
   (b3   -> o)
   (c3   -> o)
   (a3   -> o)
   (b4   -> o)
   (c4   -> o)
   (a4   -> o)
   (b5   -> o)
   (c5   -> o)
   (a5   -> o)
   (b6   -> o)
   (c6   -> o)
   (a6   -> o)
   (b7   -> o)
)
(RULES
   a1 -> b1
   a1 -> c1
   b1 -> b2
   c1 -> c2
   a2 -> b2
   a2 -> c2
   b2 -> b3
   c2 -> c3
   a3 -> b3
   a3 -> c3
   b3 -> b4
   c3 -> c4
   a4 -> b4
   a4 -> c4
   b4 -> b5
   c4 -> c5
   a5 -> b5
   a5 -> c5
   b5 -> b6
   c5 -> c6
   a6 -> b6
   a6 -> c6
   b6 -> b7
   c6 -> b7
   b7 -> b1
   b7 -> c1
)