Renardy, Michael; Rogers, Robert C.: An introduction to
partial differential equations. Second edition.
Texts in Applied Mathematics, 13. Springer-Verlag,
New York, 2004. xiv+434 pp. ISBN: 0-387-00444-0
Evans, Lawrence C.: Partial differential equations.
Graduate Studies in Mathematics, 19.
American Mathematical Society, Providence, RI, 1998.
xviii+662 pp. ISBN: 0-8218-0772-2