“…For the case m = 3, we consider O = (0, π)3 , O 0 = (0, π) × 0, π and Γ 1 = {0} × (0, π)2 . Again, the eigen-functions are generically given by a triple (i, j, k) ∈ (N * ) 3 by setting φ(x, y, z) = 2 sin(ix) sin(jy) sin(kz) (ordered first according to the distance to origin, then according to the first, then the second component).…”