Elliptic Partial Differential Equations of Second Order (2nd ed. 1983. Corr. 3rd printing)

From the reviews: "This is a book of interest to any having to work with differential equations, either as a reference or as a book to learn from.

The authors have taken trouble to make the treatment self-contained.

It (is) suitable required reading for a PhD student." --New Zealand Mathematical Society, 1985