anchor.diff:  
     name-symbol |
     ( name-symbol [ (:conc-name conc-name ) ]
  -                [ (:predicate predicate-name ) ] )
  +                [ (:predicate predicate-name ) ]
  +                class-option* )
   
   SUPERS - a list of super classes passed directly to DEFCLASS.
   
  
positive.code:                   (defmethod ,predicate ((,obj t)) nil)))
                nil))
      `(prog1
           (defclass ,class-name ,supers ,slots)
         ,@predicate-forms)))
  
  ;; Copyright (c) 2002-2006, Edward Marco Baringer
  
negative.code:                      (cdr (ensure-list name-and-options))
                       supers slots))
  
  (defun generate-defclass (class-name options supers slots)
    (let ((conc-name nil)
          (predicate nil)
          (predicate-forms nil)
          (class-options '()))
      (loop
         for (option-name . args) in options
         do (case option-name
              (:conc-name
               (when conc-name
                 (error "Can't specify the :CONC-NAME argument more than once."))
  