; Family relations knowledge base in KIF

; Define gender relations
(male Fred)
(male John)
(male Bob)
(female Martha)
(female Joan)
(female Betty)
(female Alice)

; Define parent relationships
(parent Fred Martha)
(parent Fred John)
(parent Joan Bob)
(parent Alice Bob)

; Define the father relation
(defrelation father (?x ?y)
  (and (male ?x)
       (parent ?x ?y)))

; Define the mother relation
(defrelation mother (?x ?y)
  (and (female ?x)
       (parent ?x ?y)))

; Define siblings
(defrelation sibling (?x ?y)
  (exists (?z)
    (and (parent ?z ?x)
         (parent ?z ?y)
         (not (= ?x ?y)))))