anchor.diff:  
   ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
   ;;;
  -;;; Class RPLACD-AST
  +;;; Class RPLACD-AST.
   ;;;
   ;;; This AST can be used to implement the function RPLACD and the
   ;;; function (SETF CDR) in implementations where it is a function.
  
positive.code: 
  (defmethod object-ast ((ast rplacd-ast))
    (second (children ast)))
  
negative.code: 
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  ;;;
  ;;; Class RPLACA-AST.
  ;;;
  ;;; This AST can be used to implement the function RPLACA and the
  ;;; function (SETF CAR) in implementations where it is a function.
  