public override ISet <string> tokens <T1>(IEnumerable <T1> iterable)
        {
            Multiset <string> tokens = HashMultiset.create();
            int index = 0;

            foreach (object item in iterable)
            {
                tokens.add((index++).ToString());
                tokens.addAll(fieldValues(item));
            }
//JAVA TO C# CONVERTER TODO TASK: Most Java stream collectors are not converted by Java to C# Converter:
            return(tokens.Where(token => tokens.count(token) == 1).collect(toImmutableSet()));
        }