(VAR X)
(RULES 
active(f(f(X))) -> mark(c(f(g(f(X)))))
active(c(X)) -> mark(d(X))
active(h(X)) -> mark(c(d(X)))
mark(f(X)) -> active(f(mark(X)))
mark(c(X)) -> active(c(X))
mark(g(X)) -> active(g(X))
mark(d(X)) -> active(d(X))
mark(h(X)) -> active(h(mark(X)))
f(mark(X)) -> f(X)
f(active(X)) -> f(X)
c(mark(X)) -> c(X)
c(active(X)) -> c(X)
g(mark(X)) -> g(X)
g(active(X)) -> g(X)
d(mark(X)) -> d(X)
d(active(X)) -> d(X)
h(mark(X)) -> h(X)
h(active(X)) -> h(X)
)