Received: 14 November 2019
Accepted: 17 June 2020
First Online: 6 July 2020
Compliance with ethical guidelines
: U. Lindemann, K. Sczuka, C. Becker and J. Klenk declare that they have no competing interests.
: Ethical approval was not required, because no data on human subjects or animals were collected. All data are available on personal request from the corresponding author.