/** 
     * Constructs a new automaton that accepts the complement of the language of this automaton. 
     * The input automaton is unmodified.
     */
    public FA complement() {
        FA f = (FA) clone();
        Set<State> s = new HashSet<State>();
        s.addAll(f.states);
        s.removeAll(f.accept);
        f.accept = s;
        return f;
    }