(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(X))) -> mark(X) 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)) )