; Grandparent function from page 184 of Cooke
(defun gp (X)
 (cond
  ((null (get X 'child))   NIL)
  (T                       (get(get X 'child) 'child) )
 )
)

; Tests
(putprop 'mary 'sam 'child )
(putprop 'sam 'bob 'child)
(print '(gp 'mary))
(print (gp 'mary))