SGEM 2019. 19th international multidisciplinary scientific geoconference. Vol. 19. Ecology, economics,education and legislation Issue: 5.4. 1.vyd. Sofia SGEM world science 2019. 420 s. Dostupné na internete: <www.sgemworld.at> ISBN 978-619-408-87-4. ISSN 1314-2704.