Keller, H. J. (1993). Who is who in service to the Earth. People. Projects. Organizations. Key words. Over 8000 listings a cross-indexes of people, projects and organizations, dedicated to a sustainable future (2nd ed.). VisionLink Education Foundation.
Chicago-Zitierstil (17. Ausg.)Keller, Hans J. Who Is Who in Service to the Earth. People. Projects. Organizations. Key Words. Over 8000 Listings a Cross-indexes of People, Projects and Organizations, Dedicated to a Sustainable Future. 2nd ed. München: VisionLink Education Foundation, 1993.
MLA-Zitierstil (9. Ausg.)Keller, Hans J. Who Is Who in Service to the Earth. People. Projects. Organizations. Key Words. Over 8000 Listings a Cross-indexes of People, Projects and Organizations, Dedicated to a Sustainable Future. 2nd ed. VisionLink Education Foundation, 1993.