(VAR X X1 X2 Y )
(RULES 
        active(f(g(X), Y)) -> mark(f(X, f(g(X), Y)))
        active(f(X1, X2)) -> f(active(X1), X2)
        active(g(X)) -> g(active(X))
        f(mark(X1), X2) -> mark(f(X1, X2))
        g(mark(X)) -> mark(g(X))
        proper(f(X1, X2)) -> f(proper(X1), proper(X2))
        proper(g(X)) -> g(proper(X))
        f(ok(X1), ok(X2)) -> ok(f(X1, X2))
        g(ok(X)) -> ok(g(X))
        top(mark(X)) -> top(proper(X))
        top(ok(X)) -> top(active(X))
        
)