Exercise 4.65.  Cy D. Fect, looking forward to the day when he will rise 
in the organization, gives a query to find all the wheels (using the 
wheel rule of section 4.4.1):

(wheel ?who)

To his surprise, the system responds

;;; Query results:
(wheel (Warbucks Oliver))
(wheel (Bitdiddle Ben))
(wheel (Warbucks Oliver))
(wheel (Warbucks Oliver))
(wheel (Warbucks Oliver))

Why is Oliver Warbucks listed four times?

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The wheel rule is:

(rule (wheel ?person)
      (and (supervisor ?middle-manager ?person)
           (supervisor ?x ?middle-manager)))

Oliver supervises Ben, Scrooge, and Aull.  Of these, Ben supervises 
three people, and Scrooge supervises one person.  As a result there are 
four distinct sets of bindings for ?middle-manager and ?x that satisfy 
the wheel rule while ?person is bound to (Warbucks Oliver).