“…The Poisson problem with mixed Dirichlet-Neumann boundary conditions arises naturally in connection to a series of important problems in mathematical physics and engineering dealing with conductivity, heat transfer, wave phenomena, electrostatics, metallurgical melting, and stamp problems in elasticity and hydrodynamics. Specific references can be found in [1], [12], [13], [17], [22], [23], [27], [33], [36], [42], [43], [46], [47], [48], [49], [50], [57]. Other interesting, physically relevant mixed boundary value problems are those associated with the Maxwell equations and the Dirac operator.…”