build a:1,b:2,c:3,d:4 ---- iter first next next next next ---- . iter seek-ge a next next next next ---- . iter seek-ge b next next next ---- . iter seek-ge c next next ---- . iter seek-ge d next ---- . iter seek-ge e ---- . iter seek-ge b seek-ge c seek-ge d seek-ge e ---- . iter last prev prev prev prev ---- . iter seek-lt e prev prev prev prev ---- . iter seek-lt d prev prev prev ---- . iter seek-lt c prev prev ---- . iter seek-lt b prev ---- . iter seek-lt a prev next ---- .. iter seek-ge d next next prev ---- .. iter seek-lt d seek-lt c seek-lt b seek-lt a ---- . iter globalSeqNum=1 first next next next next ---- . iter globalSeqNum=10 first next next next next ---- .