“…x 2 is clearly M-elliptic, as operator in S · M , M (R 2 ), while the Schrödinger operator i∂ x 1 − ∂ 2 , where V (P) = (0, 0), (3, 0), (2, 2), (0, 3) are the vertices of a complete Newton polyhedron. Roughly speaking the normal vector to any face of P not lying on the coordinate axes has not zero components, see [5, §1.1], [10]. Moreover again from [5, §1.1], we have that the formal order of λ(ξ ) is μ = 6.…”