Which math book(s)/textbook(s) were the most valuable to you knowledge and skill development wise? In a sense, making even more math topics much more easier for you to understand.<p>Like, for me, Spivak's Calculus and Hubbard and Hubbard's Linear Algebra + Multivariable Calculus literally gave me wings. I began visualising problems in terms of matrices and transformations. Later I read Jaynes Probability Theory with much more ease. Because I got into thinking mathematically.
I don't think there exist any book qualified as "textbook" except this one. Discrete Math by Oscar Levin.<p><a href="https://discrete.openmathbooks.org/dmoi3/" rel="nofollow noreferrer">https://discrete.openmathbooks.org/dmoi3/</a><p>No left as exercise bullshit, no prove yourself bullshit, etc. Everything is explained thoughtfully and multiple times in the book, to ensure the readers really get the idea of the subject.
Not really a math book but I really enjoyed "Genius At Play", a biography of John H. Conway.<p>Also anything from Raymond Smullyan (logic musings/riddles).