Picture 4: Model Tree of a Queuing System. Explaining Prev and Next atom references
Now look at picture 3 and the examples on prev and next.
There are a few commands often used for control and related to channels:
out(e1,e2) refers to the atom connected to output channel e l of atom e2
in(e1,e2) refers to the atom output of input channel e1 of e2
Open Output (e1) opens the general output of atom e1
Close Output (e1) closes the general output of atom e1. If closed, the channels cannot be ready,
In a similar way you can define Open Input and Close Input.
Take a look at picture 5 regarding the use of in and out: