“…A large literature has been devoted to the study of these axisymmetric and non-axisymmetric fronts in the recent years. For symmetry, uniqueness, stability and further qualitative properties of these traveling fronts, we refer to [34,36,37,51,52,56,66,68] (see also [39] for the existence of conical-shaped fronts for some systems of reaction-diffusion equations and for angles α close to π/2). When N ≥ 2 and f fulfills (1.4) with c f = 0, fronts u(t, x) = φ(|x ′ |, x N − ct) with conicalshaped level sets cannot exist anymore, see [34].…”