anchor.diff:  (define-presentation-method presentation-typep (object (type character))
     (characterp object))
   
  +(defmethod presentation-type-of ((object character))
  +  'character)
  +
  +(define-presentation-method present (object (type character) stream
  +				     (view textual-view)
  +				     &key acceptably for-context-type)
  +  (declare (ignore acceptably for-context-type))
  +  (princ object stream))
  +
   (define-presentation-type string (&optional length))
   
   (define-presentation-method presentation-typep (object (type string))
  
positive.code: (define-presentation-method presentation-typep (object (type t))
    t)
  
  (define-presentation-type nil ())
  
  (define-presentation-method presentation-typep (object (type nil))
  
negative.code: 				   super-sequence super-test super-value-key)
  		t)))))
  
  (define-presentation-method present (object (type completion) stream
  				     (view textual-view)
  				     &key acceptably for-context-type)
    (declare (ignore acceptably for-context-type))
    (present object (presentation-type-of object)
  	   :stream stream :view view))
  
  (define-presentation-type-abbreviation member (&rest elements)
    (make-presentation-type-specifier `(completion ,elements)
  				    :name-key name-key
  