I agree with Philippe. However you should note, that newer OJDBC drivers (since 19.6) are under FUTC license according to:
This is a non-clickthrough license. Therefore the artefacts are also available in public repositories (in contrast to the removed older versions). E.g.
No. But maybe.
The GPL applies to all derivative works as a whole. When you modify some code, that is a derivative work and has to be GPL-licensed.
However, if you can clearly identify parts that are not derivative but entirely your creation, then you can license those parts under any other license as well, including Apache-2.
It is in theory possible that ...
If I fork a library that uses the GPL3 license and heavily modify it, can I then release the new library with an ApacheV2 license
No, you may not. Your library is still, by your own admission, a derivative of the original GPLv3 code. GPLv3 s5c says that if you convey a derivative work, you must do so under GPLv3.
I've also contacted the original project'...
This is an interesting question, because you are mixing code copyright and copyright of articles and facts, which work quite different.
The easiest parts are the facts. A mathematical proof is something that deserves academic acknowledgement, but no copyright, as it just states facts and facts cannot be copyrighted.
Describing the proof may warrant copyright....
From one of your comments:
I just checked and they don't even list a license in their repo
In that case, you have no right to use the code from that module. Try and forget everything you've seen of their code and implement the function on your own.