-\fBfinddup\fP is a command line utility to find duplicate files, files
-common to two directories or files existing in one directories and not
-in another one.
+With a single directory argument, \fBfinddup\fP prints the duplicate
+files found in it. With two directories, it prints either the files
+common to both DIR1 and DIR2, or with the not: prefix, the ones
+present in DIR1 and not in DIR2.