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:                    Not acceptable as a user-specified readtable name." name))
  	  ((let ((rt (find-readtable name)))
  	     (and rt (cerror "Overwrite existing readtable." 
  			     'readtable-does-already-exist :readtable-name name))))
  	  (t (let ((result (apply #'merge-readtables-into
  				  ;; The first readtable specified in the :merge list is
  				  ;; taken as the basis for all subsequent (destructive!)
  