+(defun notmuch-show-add-tags-worker (current-tags add-tags)
+ "Add to `current-tags' with any tags from `add-tags' not
+currently present and return the result."
+ (let ((result-tags (copy-sequence current-tags)))
+ (mapc (lambda (add-tag)
+ (unless (member add-tag current-tags)
+ (setq result-tags (push add-tag result-tags))))
+ add-tags)
+ (sort result-tags 'string<)))
+
+(defun notmuch-show-del-tags-worker (current-tags del-tags)
+ "Remove any tags in `del-tags' from `current-tags' and return
+the result."
+ (let ((result-tags (copy-sequence current-tags)))
+ (mapc (lambda (del-tag)
+ (setq result-tags (delete del-tag result-tags)))
+ del-tags)
+ result-tags))
+