anchor.diff:    (check-type named-readtable-designator named-readtable-designator)
     (check-type new-name symbol)
     (when (find-readtable new-name)
  -    (error "A readtable named ~S already exists." new-name))
  +    (cerror "Overwrite existing readtable." 
  +            'readtable-does-already-exist :readtable-name new-name))
     (let* ((read-table (ensure-readtable named-readtable-designator))
   	 (read-table-name (readtable-name read-table)))
       ;; We use the internal functions directly to omit repeated
  
positive.code:   (cond ((eq reserved-name nil)       *standard-readtable*)
  	((eq reserved-name :standard) *standard-readtable*)
  	((eq reserved-name :current)  *readtable*)
  	(t (error "No such reserved readtable: ~S" reserved-name))))
  
  (defun find-readtable (named-readtable-designator)
    "Looks for the readtable specified by NAMED-READTABLE-DESIGNATOR and 
  
negative.code: (define-condition readtable-does-not-exist (readtable-error)
    ((readtable-name :initarg :readtable-name 
  	           :initform (required-argument)
  	           :accessor missing-readtable-name
                     :type named-readtable-designatord))
    (:report (lambda (condition stream)
               (format stream "A readtable named ~S does not exist."
                       (missing-readtable-name condition)))))
  
  (define-condition readtable-does-already-exist (readtable-error)
    ((readtable-name :initarg :readtable-name
                     :initform (required-argument)
                     :accessor existing-readtable-name
                     :type named-readtable-designatord))
    (:report (lambda (condition stream)
               (format stream "A readtable named ~S already exists."
                       (existing-readtable-name condition)))))
  
  
  