public static string NormalizeIndexWord(string input)
        {
            if (input == null)
            {
                return(null);
            }

            var result = FullWidthCharToHalfWidthChar(input);

            result = RemoveSpecialCharacters(result);
            result = new EnglishPorter2Stemmer().Stem(result).Value;
            result = result.ToLower();

            return(result);
        }