Z_, or equivalently
represents the set of integers.
The four basic sets are assigned to the identifiers
C_ during system initialization.
The set of positive integers, too, is assigned to the identifier
system initialization. It is not represented by a basic set but by
the intersection of
Z_ and the interval
The domain of basic sets know about the basic arithmetical and set-theoretic functions:
J:=Dom::Interval(3/2, 21/4): Z_ intersect J