  We present a simple group theory explanation of the fact that the energy
bands merge in the corners of the Brillouin zone for graphene and for two
particular cases of Kagome lattice for arbitrary tight--binding Hamiltonian. We
connect the linearity of the spectrum in the vicinity of these points for
monolayer graphene, bilayer graphene for AA stacking and Kagome lattice with
the properties of the conical points of the surface, known from geometry.
