anchor.diff:  
   ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
   ;;;
  -;;; Unbound cells.
  -;;;
  -;;; We do not have a single universal bit pattern indicating that a
  -;;; cell is unbound.
  -;;; 
  -;;; In the native environment, we use a special immediate value for
  -;;; variable values and slot values.  In the cross compiler, we use a
  -;;; unique CONS cell.
  -
  -(cl:defvar +unbound+ (list nil))
  -
  -;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  -;;;
   ;;; Global environment.
   ;;;
   ;;; The global environment is divided into namespaces, but a namespace
  
positive.code: ;;; symbol macro entries.
  
  (defclass simple-environment ()
    (;; The package namespace.  A list of packages.
     (%packages :initform '() :accessor packages)
     ;; The class namespace.  A list of classes.
     (%classes :initform '() :accessor classes)
  
negative.code:    (%specialp :initform nil :accessor specialp)
     ;; This slot contains the value associated with the variable.  If
     ;; there is no value associated with the variable, then this slot
     ;; contains the contents of the UNBOUND slot in the environment.
     (%value :initarg :value :accessor value)
     ;; The value of this slot is either a macro function, or NIL if
     ;; this entry does not currently represent a symbol macro.
     (%macro-function :initform nil :accessor macro-function)
  