;; demonstrate that pellet reasoner can infer that an individual exists
;; even if it is not instantiated. Being able to do queries such as the following
;; is one of the differences between using pellet to process the query versus versus 
;; using jena, even when backed by pellet.

(with-ontology some-exists? ()
    ((object-property !holds)
     (class !holder :partial (restriction !holds (min-cardinality 1)))
     (individual !alan (type !holder)))
  (princ (abstract-syntax some-exists?))
  (let ((*default-kb* (kb some-exists?)))
    (describe-entity !alan)
    (sparql '(:select (?who)()  (?who :a !holder)) 
	    :trace "show holders")
    (sparql '(:select (?who)()  (?who !ex:holds :_)) :use-reasoner :jena
	    :trace "non distinguished variable using jena")
    (sparql '(:select (?who)()  (?who !ex:holds ?what)) :use-reasoner :pellet
	    :trace "distinguished variable using pellet")
    (sparql '(:select (?who)()  (?who !ex:holds :_)) :use-reasoner :pellet
	    :trace "non distinguished variable using pellet")))