Fast forward 15 years and I've forgotten so much that I look at old notebooks and can't understand a fucking thing I wrote back then.
It depresses me to no end.
And I kind of despair that with the obligations I'm locked into right now, it will be nearly impossible to dedicate the time I would need to relearn it all.
The mind map in your head will start reconnecting fairly quickly I imagine.
I personally find the sheer quantity and range of these free pdfs daunting, so as a renegade physics graduate I'm focusing on Hammack's The Book of Proof this summer. As you did Maths at University, you might not need elementary stuff like that having already learned the strategies for abstract proof.