This goal can act as a generator and can be resatisfied. It succeeds when term is a symbol which is the name of a KnowledgeWorks class. If term is an unbound variable it generates the names of the KnowledgeWorks classes.
(kw-class truck) ; succeeds if truck is a KW class
KnowledgeWorks and Prolog User Guide (Unix version) - 24 Mar 2017