Implementation of subsequence of words

public HashSet<string> details()
     {
         String a = "One Ring to rule them all, One Ring to find them, One Ring to bring them all and in the darkness bind them";
         String b = "find, them, all"; // list of words to search
         string[] avalues = a.Split(',');
         string[] bvalues = b.Split(',');
         HashSet<string> set = new HashSet<string>();
         int index = -1;
         bool found = false;
         string text = "";

            for (int q = 0;q < bvalues.Length; q++)
            {

                if (q == 0)
                {
                    text = avalues[q];
                    set.Add(text);
                }
                else if (q > 0)
                {
                    text = avalues[q].Substring(0, avalues[q].LastIndexOf(bvalues[q])) + bvalues[q];
                    set.Add(text);
                }

            }

        char[] split = new char[] { ' ', '\t', '\r', '\n', '.', ';', ',', ':', };

        for (int r = 0; r <= set.Count-1; r++)
        {
            string setelem = set.ElementAt(r - 1); ;
              {
                string[] parts = set.ElementAt(r).Split(split, StringSplitOptions.RemoveEmptyEntries);
                foreach (string part in parts)

                    //construct the string to delete
                    if (set.ElementAt(r).Contains(part))
                    {
                        int indexa = set.ElementAt(r).IndexOf(part);
                       set.ElementAt(r - 1).Remove(indexa);

                    }
            }
        }

                 return set;
             }