The generalized Friedmann model as a self-similar solution of Vlasov–Poisson equation system V. V. Vedenyapin, N. N. Fimin and V. M. Chechetkin Eur. Phys. J. Plus, 136 6 (2021) 670 Published online: 18 June 2021 DOI: 10.1140/epjp/s13360-021-01659-7