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