Degenerate Bogdanov–Takens bifurcations in a bulk viscous cosmology Asmaa Abdel Azim, Adel Awad and E. I. Lashin Eur. Phys. J. C, 80 9 (2020) 868 Published online: 20 September 2020 DOI: 10.1140/epjc/s10052-020-8384-x