Q: Any way to find out what media is not being used in a Library?

Hey FCP X community!

  Quick question:  I have a project that over time has had a large number of clips and media dropped into it.  This event has five different projects in it as well.  I would love to thin out the entire Library by finding out what media is being used by those projects and deleting everything else.

  Is there a way to do that easily, or, export a new Library with only the projects and media being used?  I don't want all the extraneous stuff but don't want to delete something that's being used.

  My system is a MacPro, running the latest El Cap release (10.11.4) and the latest version of FCP X (10.2.3).

Thank you!
Daniel