A query to find all the wheels

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?