There was a book that I think somebody mentioned a while ago in a comment on some post somewhere here but I lost the pdf link to it when I cleared my browser history. It was by a former IOI or IMO winner about several fields of abstract math and their connections. Googling didn't help much so I'm hoping somebody knows the book.
It would help if you specified whether the book is a textbook, if it's a dead tree book or ebook, or if it might even be an online "book" like the Stacks Project: https://stacks.math.columbia.edu/
