private static INfa Union(INfa first, INfa second)
        {
            var start = new NfaState();
            start.AddTransistion(new NullNfaTransition(first.Start));
            start.AddTransistion(new NullNfaTransition(second.Start));

            var end = new NfaState();
            var endTransition = new NullNfaTransition(end);
            first.End.AddTransistion(endTransition);
            second.End.AddTransistion(endTransition);

            return new Nfa(start, end);
        }
        private static INfa KleeneStar(INfa nfa)
        {
            var start = new NfaState();
            var nullToNfaStart = new NullNfaTransition(nfa.Start);

            start.AddTransistion(nullToNfaStart);
            nfa.End.AddTransistion(nullToNfaStart);

            var end = new NfaState();
            var nullToNewEnd = new NullNfaTransition(end);

            start.AddTransistion(nullToNewEnd);
            nfa.End.AddTransistion(nullToNewEnd);

            return new Nfa(start, end);
        }