diff-backup
diff-backup is an interactive autoloaded compiled Lisp function in `diff.el
'.
(diff-backup FILE &optional SWITCHES)
Diff this file with its backup file or vice versa.
Uses the latest backup, if there are several numerical backups.
If this file is a backup, diff it with its original.
The backup file is the first file given to `diff'.
With prefix arg, prompt for diff switches.