код говно

SkipListLables oldLable;
if (!(previousNode.NextReference.Get(out oldLable) is SkipListTailNodeWithBacklink<TElement>))
   while (oldLable.HasLable(SkipListLables.Mark))
   {
       previousNode = previousNode.Backlink;
       previousNode.NextReference.Get(out oldLable);
   }