Apostol? Courant? Heh, I feel sorry for you 120IQ people. The only Calculus book that should be considered 'hard' and 'worthy' is Sternberg, all others are child's play in comparison.

It truly is amazing how they managed to create a book that only the true intelligent people can understand, you could say Apostol and Courant are a little hard in comparison to most math textbooks out there, but even with some effort, a brainlet can still go through them with certain ease, but Loomis and Sternberg's Calculus is on a whole nother level.