Remove the files unless you have clearance from the copyright owners

[oneiros-de]

I'm pretty sure e.g. Knuth has not given you permission.

[kbelcher3]

Let Knuth file a DMCA complaint if he so chooses.

[joshua-koehler]

Its a bit more nuanced, but this shouldn't be posted at least without a proviso. See nice summary of US Copyright on fair use laws. You can use a small section, but if this is used in place of buying the book, it violates the spirit and letter of copyright laws. I deliberated on this, and decided the only right thing to do was to buy the book, which I just did. So I feel free to use this when I want to do a quick text-search to find a chapter in my hard-copy.

[djtrack16]

I agree with @joshua-koehler.

A simple Google search shows that PDFs of his texts are freely available in many, many places on the net.
I will add a condition/proviso to the README urging people who find this repo useful to not use it in lieu of buying the actual books. Aka "please buy the book and only use this repo as a reference/favorites"
Personally, I hate reading technical/mathematical/scientific texts online anyway, so you need the hardcopy to do any "substantial work" (YMMV).