Hello! I am an undergraduate student majoring in the chemistry and microbiology. Summer vacation is truly a great time to teach myself some some subjects besides conducting the scientific research, and I am decided to self-study the calculus over this summer (I took the introductory calculus but the course was not too deep but focused only on the general problem-solving). I am planning to purchase some "deep, proof-based, and rigorous" calculus textbooks because I realized that physical chemistry, quantum mechanics, and physics (and chemistry itself) that I have to take later on really depend on the proof-based calculus. I am also thinking of purchasing one or two books from Spivak, Courant, Lang, or Apostol (I like to buy all of them but each costs a lot). What calculus textbook from above do you recommend to me? I am planning to finish the book by the end of the summer vacation. If you also know a calculus textbook that is dedicated to the chemistry, please let me share your information too. Have a wonderful day!