public java.util.List<A> subList(int fromIndex, int toIndex) {
        if  (fromIndex < 0 || toIndex > size() || fromIndex > toIndex)
            throw new IllegalArgumentException();

        ArrayList<A> a = new ArrayList<A>(toIndex - fromIndex);
        int i = 0;
        for (List<A> l = this; l.tail != null; l = l.tail, i++) {
            if (i == toIndex)
                break;
            if (i >= fromIndex)
                a.add(l.head);
        }

        return Collections.unmodifiableList(a);
    }