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