© 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

Creative Commons-lisensen er mer spesifikt Attribution 4.0 International (CC BY 4.0).
Med mindre annet er angitt, så er denne innførselen lisensiert som © 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). Creative Commons-lisensen er mer spesifikt Attribution 4.0 International (CC BY 4.0).