(VAR X X1 X2)
(RULES 
active(h(X)) -> mark(g(X,X))
active(g(a,X)) -> mark(f(b,X))
active(f(X,X)) -> mark(h(a))
active(a) -> mark(b)
mark(h(X)) -> active(h(mark(X)))
mark(g(X1,X2)) -> active(g(mark(X1),X2))
mark(a) -> active(a)
mark(f(X1,X2)) -> active(f(mark(X1),X2))
mark(b) -> active(b)
h(mark(X)) -> h(X)
h(active(X)) -> h(X)
g(mark(X1),X2) -> g(X1,X2)
g(X1,mark(X2)) -> g(X1,X2)
g(active(X1),X2) -> g(X1,X2)
g(X1,active(X2)) -> g(X1,X2)
f(mark(X1),X2) -> f(X1,X2)
f(X1,mark(X2)) -> f(X1,X2)
f(active(X1),X2) -> f(X1,X2)
f(X1,active(X2)) -> f(X1,X2)
)