(VAR X X1 X2 )
(RULES 
        active(f(0)) -> mark(cons(0, f(s(0))))
        active(f(s(0))) -> mark(f(p(s(0))))
        active(p(s(0))) -> mark(0)
        active(f(X)) -> f(active(X))
        active(cons(X1, X2)) -> cons(active(X1), X2)
        active(s(X)) -> s(active(X))
        active(p(X)) -> p(active(X))
        f(mark(X)) -> mark(f(X))
        cons(mark(X1), X2) -> mark(cons(X1, X2))
        s(mark(X)) -> mark(s(X))
        p(mark(X)) -> mark(p(X))
        proper(f(X)) -> f(proper(X))
        proper(0) -> ok(0)
        proper(cons(X1, X2)) -> cons(proper(X1), proper(X2))
        proper(s(X)) -> s(proper(X))
        proper(p(X)) -> p(proper(X))
        f(ok(X)) -> ok(f(X))
        cons(ok(X1), ok(X2)) -> ok(cons(X1, X2))
        s(ok(X)) -> ok(s(X))
        p(ok(X)) -> ok(p(X))
        top(mark(X)) -> top(proper(X))
        top(ok(X)) -> top(active(X))
        
)