All applications are required to maintain the list of next leaf tasks. Before modifying the task structure, the application must set the lot's task structure modified time to the current time. Then, modifications to the task tree are to be made prior to the required changes in the next leaf pointers. Note that the lot's list of ready tasks are treated as individual task trees and that the task next leaf pointer for the last leaf task in a task tree is nil. This is indicated in Figure 1 .
Tasks also have a list of planopinsts.
These planopinsts are precomputed at lot start time in order to make it faster for operate machine to start up. Part of its definition is shown below to specify the possible arguments to this procedure. The lot argument is required. The second argument is optional and should be t if you want some printout or nil if you want it to work in silence. The optional keywords enable the creation of planopinsts, the clean up of old planopinsts and the reinitialization of the lot's list of ready tasks.