/**
     * Runs the given string on this automaton. [Martin, Def. 3.14]
     * @param s a string
     * @return true iff the string is accepted
     * @exception IllegalArgumentException if a symbol in <tt>s</tt> is not in the alphabet
     */
    public boolean accepts(String s) throws IllegalArgumentException {
        Set<State> set = deltaStar(initial, s);
        set.retainAll(accept);
        return !set.isEmpty();
    }