private SubExpression DoConvert(string regex)
        {
            Tokens = RegexTokenizer.Tokenize(regex);
            SubExpression subExpression = And();

            return(subExpression);
        }
        public static List <Token> Tokenize(string regex)
        {
            RegexTokenizer tokenizer = new RegexTokenizer();

            return(tokenizer.DoTokenize(regex));
        }