Topological states of non-Hermitian systems V.M. Martinez Alvarez, J.E. Barrios Vargas, M. Berdakin and L.E.F. Foa Torres Eur. Phys. J. Special Topics, 227 12 (2018) 1295-1308 Published online: 18 October 2018 DOI: 10.1140/epjst/e2018-800091-5