Funding for this research was provided by:
Staedtler Stiftung (WW/eh 01/15)
Dr. Pfleger Stiftung in Bamberg (Schreiben vom 05.12.2018)
Received: 23 October 2019
Accepted: 14 January 2020
First Online: 7 February 2020
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: The author declares that he has no competing interests.