Rare and hidden attractors in Van der Pol-Duffing oscillators S. Brezetskyi, D. Dudkowski and T. Kapitaniak Eur. Phys. J. Special Topics, 224 8 (2015) 1459-1467 Published online: 27 July 2015 DOI: 10.1140/epjst/e2015-02471-2