initial sights

terminal sights

• Think of a primitive as an “elementary”
process that **transforms** the initial
“objects” into terminal ones: it is a symbolic “notation” of a
typically nontrivial process (structured event).

• The circle and the square denote two site types: letters {a, b} and {x, y} are names of the variables that are allowed to vary over
non-overlapping sets of numeric labels.

• Brackets [ ] signify that we are, in fact,
dealing with a class of (original) primitives, where each original primitive carries concrete
numeric labels.