public IReadOnlySortedList <TKey, T> GetIndexList <TKey>(ISortedIndex <TKey> index)
 {
     throw new NotImplementedException();
 }
 public IOrderedEnumerable <T> GetSortedValues <TKey>(TKey key, ISortedIndex <TKey> index)
 {
     throw new NotImplementedException();
 }
 public void AddUniqueSortedIndex <TKey>(ISortedIndex <TKey> index)
 {
     throw new NotImplementedException();
 }