School of Mathematical Sciences, Peking University, Beijing 100871, People's Republic of China ; School of Mathematical Sciences, Peking University, Beijing 100871, People's Republic of China
Abstract:
We study the boundary regularity in the Dirichlet problem of the differential operators
Our main result is: if is neither an integer nor a half-integer not less than , one cannot expect global smooth solutions of ; if satisfies , then must be either a polynomial of degree at most or a polyharmonic function of degree .