35Axx General topics
 35A01 Existence problems: global existence, local existence, nonexistence
 35A02 Uniqueness problems: global uniqueness, local uniqueness, nonuniqueness
 35A08 Fundamental solutions
 35A09 Classical solutions
 35A10 CauchyKovalevskaya theorems
 35A15 Variational methods
 35A16 Topological and monotonicity methods
 35A17 Parametrices
 35A18 Wave front sets
 35A20 Analytic methods, singularities

35A21 Propagation of singularities
(1)
 35A22 Transform methods (e.g. integral transforms)
 35A23 Inequalities involving derivatives and differential and integral operators, inequalities for integrals
 35A24 Methods of ordinary differential equations
 35A25 Other special methods
 35A27 Microlocal methods; methods of sheaf theory and homological algebra in PDE [See also 32C38, 58J15]
 35A30 Geometric theory, characteristics, transformations [See also 58J70, 58J72]
 35A35 Theoretical approximation to solutions (For numerical analysis, see 65Mxx, 65Nxx)
 35A99 None of the above, but in this section