terms of influencing or controlling dynamical systems [@Bollt; @Gora] in a certain way.

Acknowledgements
================

One of the authors (P.S.) thanks the Max-Planck Institute for Physics of Complex Systems in Dresden for its kind hospitality. D.P. acknowledges financial support by the Deutsche Forschungsgemeinschaft and the Landesgraduiertenförderungsgesetz (LGFG).

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