584 Jacques Chazarain/Alain Piriou: Introduction to the theory of linear 
partial differential equations. North-Holland 1982.

J. Duistermaat: Fourier integral equations. Birkhaeuser 1995, 160p. DM 68.

O. Grudzinski: Quasihomogeneous distributions.
North-Holland 1991, 450p. Dfl. 225.

Lars Hoermander: Notions of convexity.
Birkhaeuser 1994, 430p. 3-7654 (or 7643 ?) -3799-0. The main purpose of this 
book is to discuss notions of convexity that are found in the theory of 
partial differential equations and complex analysis.

Andy Magid: Differential Galois theory.
Notices AMS October 1999, ...

11046 Detlef Mu''ller: Differentialoperatoren zweiter Ordnung
und harmonische Analysis. Jber. DMV 99 (1997), 149-163.

V. Nazaikinskii/V. Shatalov/B. Sternin: Contact geometry and linear 
differential equations. De Gruyter 1992, 210p. DM 138.

21103 Francois Treves: Basic linear partial differential equations.
Dover 2006, 470p. Eur 21.