(SIG
   (b   -> o)
   (a   -> o)
   (c   -> o)
   (d   -> o)
   (e   -> o)
   (f   o o -> o)
   (A   -> o)
)
(RULES
   b -> a
   b -> c
   c -> c
   d -> c
   d -> e
   f(x,a) -> A
   f(x,e) -> A
   f(x,A) -> A
   f(c,x) -> A
)