Photon splitting in strongly magnetized medium with taking into account positronium influence R.A. Anikin, M.V. Chistyakov, D.A. Rumyantsev and D.M. Shlenev EPJ Web Conf., 191 (2018) 08011 Published online: 31 October 2018 DOI: 10.1051/epjconf/201819108011