(let ((topic (gnus-current-topic)))
(list topic
(read-string (format "Rename %s to: " topic)))))
+ ;; Check whether the new name exists.
+ (when (gnus-topic-find-topology new-name)
+ (error "Topic '%s' already exists"))
+ ;; Do the renaming.
(let ((top (gnus-topic-find-topology old-name))
(entry (assoc old-name gnus-topic-alist)))
(when top