Text and Data Mining valid from 2019-05-09
Received: 21 March 2019
Accepted: 25 April 2019
First Online: 9 May 2019
Compliance with ethical standards
: Eriko Aoki declares that she has no conflict of interest. Masamichi Ikeguchi declares that he has no conflict of interest.
: This article does not contain any studies with human participants or animals performed by any of the authors.