Main Textbook: Walter A. Strauss, Partial Differential
Equations: An Introduction, John Wiley & Sons (1992).Author's
errata list.
Further Reading:
Lawrence C. Evans, Partial differential equations.Graduate Studies in Mathematics, 19. American Mathematical Society, Providence, RI, 1998. Author's errata list.
Gerald B. Folland, Introduction to partial differential equations. Second edition. Princeton University Press, Princeton, NJ, 1995.