(SIG
   (a   -> o)
   (c   -> o)
   (h   o o -> o)
   (b   -> o)
   (f   o -> o)
)
(RULES
   a -> c
   a -> h(c,a)
   h(b,f(c)) -> b
   c -> h(a,h(h(b,a),a))
)