This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 (BY-NC-ND) which means that the text may be used for non-commercial purposes, provided credit is given to the author. For details go to http://creativecommons.org/licenses/by-nc-nd/4.0/ To create an adaptation, translation, or derivative of the original work and for commercial use, further permission is required and can be obtained by contacting rights@ transcript-verlag.de Creative Commons license terms for re-use do not apply to any content (such as graphs, figures, photos, excerpts, etc.) not original to the Open Access publication and further permission may be required from the rights holder. The obligation to research and clear permission lies solely with the party re-using the material.