Sublime
An inspiration engine for ideas
Since folks are asking:
The books I mentioned on @xai spaces are "Linear Algebra Done Right" by Axler and "Naive Set Theory" by Halmos. Other math books that I really enjoyed over the years:
"Introduction to Algorithms" by Thomas H. Cormen & Charles E. Leiserson & Ronald L. Rivest & Clifford... See more
Greg Yangx.com