 
 
 
5.2  Set Variables
Set variables are variables which can eventually take a ground integer
set as their value. They are characterized by a lower bound (the set
of elements that are definitely in the set) and an upper bound (the
set of elements that may be in the set). A set variable can be
declared as follows: 
        SetVar :: []..[1,2,3,4,5,6,7]
If the lower bound is the empty set (like in this case) this can be written as 
        SetVar subset [1,2,3,4,5,6,7]
If the lower bound is the empty set and the upper bound is a set of
consecutive integers, one can also declare it like
        intset(SetVar, 1, 7)
which is equivalent to the above. 
The predicates to declare sets are:
- 
?Set :: ++Lwb..++Upb
- 
 Set is an integer set within the given bounds 
- intset(?Set, +Min, +Max)
- 
 Set is a set containing numbers between Min and Max 
- intsets(?Sets, ?N, +Min, +Max)
- 
 Sets is a list of N sets containing numbers between Min and Max 
Set variables are by default printed in a particular way, e.g.
?- X :: [2,3]..[1,2,3,4], write(X).
X{[2, 3] \/ ([] .. [1, 4]) : _308{[2 .. 4]}}
The curly brackets contain
- 
the lower bound of the set
- the union symbol
- the set of optional values (that may or may not be in the set)
- a colon
- a finite domain indicating the admissible cardinality for the set
5.2.3  Domain Access
- 
potential_members(?Set, -List)
- 
 List is the list of elements of whose membership in Set is currently uncertain 
- set_range(?Set, -Lwb, -Upb)
- 
 Lwb and Upb are the current lower and upper bounds on Set 
 
 
