Text and Data Mining valid from 2018-02-22
Received: 22 December 2017
Accepted: 16 February 2018
First Online: 22 February 2018
Compliance with ethical standards
: The authors declare no conflict of interest.
: For this type of study formal consent is not required.
: This article does not contain any studies with human participants or animals performed by any of the authors.
: The informed consent was not needed for this study.