anchor.diff:    (princ "done.")
     (terpri)
   
  +  (princ "Actual tree size:")
  +  (print (size tree))
  +  (terpri)
  +
     (princ "Does the tree contain '-42'? -> ")
     (if (contains tree -42)
         (princ "Yes")
  
positive.code:           (setf (parent riglef) n))
        (cond ((null par) (setf (root tree) rig))
              ((eql n (left par)) (setf (left par) rig))
              (T (setf (right par) rig)))))
    T
  )
  
  
negative.code:              The node to rotate over, which should not be {@code null}.
      @param deletion
               Indicator if this is a rotation after an insertion or after
               a deletion of the node."
  
    (if (and
         (eql (root tree) n)
  