Document is current

Article History

Received: 6 November 2017

Accepted: 15 June 2018

First Online: 13 July 2018

Ethics approval and consent to participate

: The research in this paper does not involve human subjects, human material, or human data; therefore, there was no need for the approval of an ethics committee nor the consent of human participants.

: Figures appearing in this paper are not related to individual participants, and therefore, there was no need for consent for publication.

: The author declares that he has no competing interests.

: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.