If true, this is concerning. The public domain is already under attack from increasingly aggressive copyright term extensions. This does touch on a point I've

If true, this is concerning. The public domain is already under attack from increasingly aggressive copyright term extensions. This does touch on a point I've been wondering about recently. Let's say I write an adaptation of Romeo and Juliet where the main characters are all robots and the setting is in space. From my understanding, I can claim copyright on my new work so long as it contains sufficient new creativity and transformation. My new work would be considered a derivative work from the public domain original, and I would hold the copyright for my work. The question is, what happens when someone else creates an adaptation of Romeo and Juliet where the main characters are all pirates and the setting is the ocean? If my work were an original, I could sue the creator of the pirate version because his version was a derivative work of mine and he didn't have my permission to create it. But obviously, he can say his is a derivative of the public domain version, not my version. How do all these rights interact? My mind gets tied up in knots trying to work it out.