How to maintain lists ?

To return from a high list level to the next-lower level (SY-LSIND), the user chooses
Back on a secondary list.The system then releases the currently displayed list and
activates the list created one step earlier.The system deletes the contents of the
released list.To explicitly specify the list level into which you want to place output, set the
SY-LSIND field. The system accepts only index values which correspond to existing list
levels.It then deletes all existing list levels whose index is greater or equal to the index
you specify.For example, if you set SY-LSIND to 0, the system deletes all secondary
lists and overwrites the basic list with the current secondary list.