Spivak’s Calculus reignited my interest and appreciation in math. Sad to discover the author passed away quite recently. The way of explaining principles and making you do the hard work via problems which I believe is a must with this book, is profoundly astonishing. There’s a lot of mathematical insight packed into those problems, it almost feels you can build up the entire high school and the early uni curriculum from the ground up, for instance there are a number of popular formulas you’d arrive at and derive accidentally while working on those problems. Furthermore it really works your brains by making sure you can reason within the established framework and exercise great doubt. I’m taking this book very slowly.