Text and Data Mining valid from 2019-02-08
Received: 24 October 2018
Revised: 23 January 2019
Accepted: 28 January 2019
First Online: 8 February 2019
Compliance with ethical standards
: The authors declare that they have no conflict of interest.
: This article does not contain any studies with human participants or animals performed by any of the authors.
: Not applicable.