Festschrift on the occasion of Ulrike Feudel's 60th birthday Jan A. Freund, Ksenia Guseva and Celso Grebogi Eur. Phys. J. Special Topics, 226 9 (2017) 1695-1701 Published online: 21 June 2017 DOI: 10.1140/epjst/e2017-70084-6