anchor.diff:  
   (defun test ()
     (test/list-lengths)
  -  (test/list-elements))
  -
  +  (test/list-elements)
  +  (test/tree-find))
  +
  +(test)
   ;;;; THE END ;;;;
  
positive.code: 
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  
  (defun tree-difference (a b &key (test (function eql)))
    "
  RETURN: A tree congruent to A and B where each node is = when the
  
negative.code:            ;; "HASHED-REMOVE-DUPLICATES" moved to COM.INFORMATIMAGO.COMMON-LISP.CESARUM.SEQUENCE
             "ENSURE-LIST" "PROPER-LIST-P" "LIST-LENGTHS" "LIST-ELEMENTS"
             "ENSURE-CIRCULAR" "MAKE-CIRCULAR-LIST" "CIRCULAR-LENGTH"
             "TREE-FIND" "TREE-DIFFERENCE" "REPLACE-TREE" "MAPTREE")
    (:documentation
     "
  This package exports list processing functions.
  