(SIG
   (f   o -> o)
   (a   -> o)
   (g   o -> o)
)
(RULES
   f(f(f(x))) -> a
   f(f(a)) -> a
   f(a) -> a
   f(f(g(g(x)))) -> f(a)
   g(f(a)) -> a
   g(a) -> a
)