(deffacts dane
(pair 3 4)
(pair 4 5)
(triplet 4 4 6)
)

(defrule demo-not-1
(pair ?x ?y)
(pair ?y ?z)
(not (triplet ?x ?y ?z))
=>
(printout t "No triplet " ?x " " ?y " " ?z " exists!" crlf)
)

(defrule demo-not-2
(not (triplet ?x ?y ?z))
(pair ?x ?y)
(pair ?y ?z)
=>
(printout t "No triplet exists at all!" crlf)
)