sdsl-lite

> The currently active fork of SDSL (https://github.com/xxsds/sdsl-lite) has a BSD license. How is that legally possible? As I understand, the GPL doesn't allow a derivative work to remove the copyleft provisions from the license. Or maybe I misunderstood your comment?

Probably the same reason as with other libraries from the academia. When all free licenses are pretty much equivalent from your point of view, choosing a license is just a bureaucratic formality. The person choosing the license usually doesn't think about the issue too much, and they probably don't have that much experience with licenses anyway. The currently active fork of SDSL (https://github.com/xxsds/sdsl-lite) has a BSD license. There was supposed to be a team developing the fork, but most people either left the academia or had their research interests move elsewhere. Now there seems to be just a single developer who maintains SDSL as a byproduct of SeqAn.

The next version, which is currently under development, will change this to BSD: https://github.com/xxsds/sdsl-lite

I'm assuming you meant GPL? I've got good news for you then, the next version is going to be under a BSD license: https://github.com/xxsds/sdsl-lite (currently unstable!)