(VAR X XS N) (RULES from(X) -> cons(X,n__from(n__s(X))) after(0,XS) -> XS after(s(N),cons(X,XS)) -> after(N,activate(XS)) from(X) -> n__from(X) s(X) -> n__s(X) activate(n__from(X)) -> from(activate(X)) activate(n__s(X)) -> s(activate(X)) activate(X) -> X )