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