*****  Insert 50...60
[50...60]

*****  Insert 70...75
[50...60]
         [70...75]

*****  Insert 74...80
[50...60]
         [70...80]

*****  Insert 10...20
         [50...60]
[10...20]         [70...80]

*****  Insert 30...40
         _________[50...60]
[10...20]                  [70...80]
         [30...40]

*****  Delete 15...55
         [56...60]
[10...14]         [70...80]