To find all music not in other playlists

There is an answer to someone else's question which has

you create a playlist folder and using that in a new smart playlist.

When you create the playlist folder, you can only include your manual playlists, not the other smart playlists. The resulting new smart playlist will include songs that are also in other smart playlists. The only way I found to do it (without scripts) is to manually select each song in this smart playlist to see if it is in another playlist (smart or manual) and to manually put it into a manual playlist of "songs not in other playlists".