solvability of various types of differential and integral equations
Cauchy-Kowalewskaya and Holmgren theorems
elliptic, hypoelliptic, hyperbolic and parabolic operators
general theory of operators in Banach spaces
variational method of solving boundary value problems involving elliptic operators
Dirichlet and Neumann type problems for the Laplacian
scientific article; zbMATH DE number 1388033