git-annex find --not --unused is currently the same as git-annex find --unused because --unused is not a file matching option. This is a bit confusing.

And it would be useful to have a way to find all keys that are not amoung the unused keys.

Given the implementation of --not is tied to file matching options, it might be best to add a new option like --used or --not-unused.

It would also perhaps be good to detect when matching options are used that don't make sense, and error out on commands like git-annex find --not or git-annex find -and -(