anchor.diff:  ;;; required, an instance of this class is created, and then never
   ;;; removed.
   
  -(defclass function-entry (base-entry named-entry)
  +(defclass function-entry (named-entry)
     (;; The value of this slot is a CONS cell in which the CAR is always
      ;; a function.  When the function is unbound, it contains the
      ;; function in the UNBOUND slot, which signals an error.
  
positive.code: 
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  ;;;
  ;;; BASE-ENTRY.
  ;;; 
  ;;; A base entry is an entry that does not refer to any other entry.
  ;;; Entries that represent functions, variables, macros, and optimize
  ;;; declarations are examples of base entries. 
  (defclass base-entry (entry)
    ())
  
  (defgeneric base-entry-p (entry))
  
  (defmethod base-entry-p (entry)
    (declare (ignore entry))
    nil)
  
  (defmethod base-entry-p ((entry base-entry))
    (declare (ignorable entry))
    t)
  
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  ;;;
  ;;; NAMED-ENTRY.
  ;;; 
  ;;; A mixin class for entries having a name associated with them. 
  
negative.code: ;;;
  ;;; Class VARIABLE-ENTRY.
  
  (defclass variable-entry (named-entry)
    (;; This slot contains true if and only if this entry represents a
     ;; constant variable.
     (%constantp :initform nil :accessor constantp)
  