“…It means that we look for a solution such that the nontangential maximal function of and ∇ are in ( Ω) and boundary conditions are fulfilled in the sense of nontangential limits. The goal of the paper is to prove results similar to the well-known results corresponding to the Laplace equation ( [4,5,[8][9][10][11][18][19][20][21]23,30,31,33,37,38,40,41,46,48]). We find necessary and sufficient conditions for the existence of an -solution of the Neumann and Robin problem for bounded and unbounded domains with compact Lipschitz boundary.…”