/** 
     * Converts this FA into an equivalent {@link NFA}. 
     * Note: this is trivial since an FA is just a special kind of NFA, except for the different representation.
     */
    public NFA toNFA() {
        NFA f = new NFA();
        f.alphabet = alphabet;
        Map<State,State> m = new HashMap<State,State>(); // map from old states to new states
        for (State p : states) {
            State s = (State) p.clone();
            f.states.add(s);
            m.put(p, s);
            if (accept.contains(p))
                f.accept.add(s);
            if (p==initial)
                f.initial = s;
        }
        for (Map.Entry<StateSymbolPair,State> e : transitions.entrySet()) {
            StateSymbolPair ssp = e.getKey();
            State q = e.getValue();
            Set<State> ns = new HashSet<State>();
            ns.add(m.get(q));
            f.transitions.put(new StateSymbolPair(m.get(ssp.state), ssp.symbol), ns);
        }
        return f;
    }