Each CLP(FD) variable has an associated set of admissible integers,
which we call the variable's domain. Initially, the domain of
each CLP(FD) variable is the set of all integers. CLP(FD)
constraints like #=/2, #>/2
and #\=/2 can at most
reduce, and never extend, the domains of their arguments. The
constraints in/2 and ins/2
let us explicitly state domains of CLP(FD) variables. The process of
determining and adjusting domains of variables is called constraint
propagation, and it is performed automatically by this library.
When the domain of a variable contains only one element, then the
variable is automatically unified to that element.
Domains are taken into account when further constraints are stated,
and by enumeration predicates like labeling/2.
