“…Such an assumption could be removed, see [22]. For D = 2 we do not impose any further condition on f , whereas for D 3 we shall consider a more restrictive class of nonlinearities, by requiring f (x, u,ū) = ∂ ∂ū H (x, u,ū) + g(x,ū), H (x, u,ū) = H (x, u,ū), (1.4) i.e.…”