Shurygin, V.V. and Shurygin, V.V. 2019. An Approach to Presentation of the Lobachevskii Geometry to Secondary School and First Year University Students. Russian Digital Libraries Journal. 22, 6 (Dec. 2019), 737-748. DOI:https://doi.org/10.26907/1562-5419-2019-22-6-737-748.