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In fact, this operator signature permits
testing not only the emptiness but also other attributes of the
HQSet. We remark that some constants such as CONSTANT_EMPTY,
CONSTANT_UNIVERSE, UNDEFINED are introduced. In the polyhedral case,
they respectively represent an empty set, e.g. with only the
constraint , all the space (), with no constraint, and an
undefined HQSet object.
The undefined HQSet object is not available in PPL, Octagon and New
POLKA but only in . In , there is a distinction between the
pointer to an undefined constraint system and a standard ANSI C
pointer. It is because sometimes programmers want to know whether the
returned object is an empty or undefined constraint system
.
Nguyen Que Duong
2006-09-16