(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)
        
)