Text and Data Mining valid from 2018-02-23
Received: 21 November 2017
Revised: 8 February 2018
Accepted: 9 February 2018
First Online: 23 February 2018
Compliance with ethical standards
: The authors declare that they have no competing interests at all. The author(s) of this article has (have) verified that its article is original and that it does not violate any other publisher’s rights nor does it contain matters that may disgrace or invade privacy.