By "in print" I mean, the publisher is actively selling it.

Although, if I were writing the law I would require selling DRM free ebooks for ebooks to count for maintaining the copyright.

So, if an e-book is listed on Amazon, does that count as "actively selling it"? It's for sale, after all. The same happens with Print On Demand (POD).

This is actually a real issue when authors have deals where rights revert to them when the book goes out of print.

https://katemckean.substack.com/p/when-does-a-book-go-out-of...

What if we applied the simple test that the book was originally published on paper and no other printings have occurred (digital or paper).