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