(note TQG7)  ;; boolean version

(instance Bill7-1 Man)
(instance Jane7-1 Woman)
(instance Bob7-1 Man)

(mother Bill7-1 Jane7-1)
(sibling Bob7-1 Bill7-1)

(query (and
         (mother Bill7-1 Jane7-1)
         (mother Bob7-1 Jane7-1)))

(answer yes)

;; (=>
;;   (and
;;     (instance ?ANIMAL1 Organism)
;;     (instance ?ANIMAL2 Organism))
;;   (<=>
;;     (sibling ?ANIMAL1 ?ANIMAL2)
;;     (and
;;       (not (equal ?ANIMAL1 ?ANIMAL2))
;;       (exists (?FATHER ?MOTHER)
;;         (and
;;           (father ?ANIMAL1 ?FATHER)
;;           (father ?ANIMAL2 ?FATHER)
;;           (mother ?ANIMAL1 ?MOTHER)
;;           (mother ?ANIMAL2 ?MOTHER))))))