A universal Hamiltonian for motion and merging of Dirac points in a two-dimensional crystalG. Montambaux, F. Piéchon, J.-N. Fuchs and M. O. GoerbigEur. Phys. J. B, 72 4 (2009) 509-520DOI: https://doi.org/10.1140/epjb/e2009-00383-0