1. Sobolev Spaces;Adams,1975
2. Set-Valued Analysis;Aubin,1990
3. R. Courant, D. Hilbert, Methods of Mathematical Physics, Wiley-Interscience, New York, 1966.
4. Partial Differential Equations;Evans,1998
5. J. Hadamard, Lectures on Cauchy's Problem in Linear Partial Differential Equations, New York, 1952.