Reading Rudin's "Principles of Mathematical Analysis" (PMA) or Pugh's "Real Mathematical Analysis" provides a solid foundation in real analysis, potentially covering all essential concepts found in Spivak's "Calculus." Engaging deeply with Rudin's exercises can ensure a comprehensive understanding, making Spivak's content largely redundant. However, for those new to proofs or studying independently, these texts may not be the most effective choices. An alternative recommended for self-study is "Numbers and Functions: Steps to Analysis," which offers a structured approach with curated problems and solutions, although it is currently out of print.