Close-to-elliptic equations Elliptic equations and elliptic systems General first-order partial differential equations and systems of first-order partial differential equations General higher-order partial differential equations and systems of higher-order partial differential equations Generalized solutions to partial differential equations General topics in partial differential equations Hyperbolic equations and hyperbolic systems Miscellaneous topics in partial differential equations Overdetermined problems for partial differential equations and systems of partial differential equations Parabolic equations and parabolic systems Partial differential equations and systems of partial differential equations with constant coefficients Partial differential equations of mathematical physics and other areas of application Partial differential equations of mixed type and mixed-type systems of partial differential equations Pseudodifferential operators and other generalizations of partial differential operators Qualitative properties of solutions to partial differential equations Representations of solutions to partial differential equations Spectral theory and eigenvalue problems for partial differential equations