Combined boundary value problems for the nonhomogeneous tri-analytic   equation
  In the present article we present a particular combination of boundary problems for the inhomogeneous tri-analytic equation: the Neumann-(Dirichlet-Neuman) problem and the (Dirichlet-Neumann)-Dirichlet problem. In order to obtain the solution and solvability conditions we use an iteration's process involving those corresponding to equations of lower order. 
Antonio N. Di Teodoro and Carmen J. Vanegas
math.CV math-ph math.MP