(VAR X XS N X1 X2) (RULES active(from(X)) -> mark(cons(X,from(s(X)))) active(after(0,XS)) -> mark(XS) active(after(s(N),cons(X,XS))) -> mark(after(N,XS)) active(from(X)) -> from(active(X)) active(cons(X1,X2)) -> cons(active(X1),X2) active(s(X)) -> s(active(X)) active(after(X1,X2)) -> after(active(X1),X2) active(after(X1,X2)) -> after(X1,active(X2)) from(mark(X)) -> mark(from(X)) cons(mark(X1),X2) -> mark(cons(X1,X2)) s(mark(X)) -> mark(s(X)) after(mark(X1),X2) -> mark(after(X1,X2)) after(X1,mark(X2)) -> mark(after(X1,X2)) proper(from(X)) -> from(proper(X)) proper(cons(X1,X2)) -> cons(proper(X1),proper(X2)) proper(s(X)) -> s(proper(X)) proper(after(X1,X2)) -> after(proper(X1),proper(X2)) proper(0) -> ok(0) from(ok(X)) -> ok(from(X)) cons(ok(X1),ok(X2)) -> ok(cons(X1,X2)) s(ok(X)) -> ok(s(X)) after(ok(X1),ok(X2)) -> ok(after(X1,X2)) top(mark(X)) -> top(proper(X)) top(ok(X)) -> top(active(X)) )