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@article{MP_2004_a9, author = {G. A. Gal'perin}, title = {{\CYRB}{\cyri}{\cyrl}{\cyrsftsn}{\cyrya}{\cyrr}{\cyrd}{\cyrn}{\cyra}{\cyrya} {\cyrf}{\cyro}{\cyrr}{\cyrm}{\cyru}{\cyrl}{\cyra} {\cyrd}{\cyrl}{\cyrya} {\cyri}{\cyrz}{\cyrm}{\cyre}{\cyrr}{\cyre}{\cyrn}{\cyri}{\cyrya} {\cyrr}{\cyra}{\cyrs}{\cyrs}{\cyrt}{\cyro}{\cyrya}{\cyrn}{\cyri}{\cyrishrt} {\cyrv}~{\cyrg}{\cyre}{\cyro}{\cyrm}{\cyre}{\cyrt}{\cyrr}{\cyri}{\cyri} {{\CYRL}{\cyro}{\cyrb}{\cyra}{\cyrch}{\cyre}{\cyrv}{\cyrs}{\cyrk}{\cyro}{\cyrg}{\cyro}}}, journal = {Matematicheskoe Prosveshchenie}, pages = {93--112}, publisher = {mathdoc}, year = {2004}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/MP_2004_a9/} }
G. A. Gal'perin. Бильярдная формула для измерения расстояний в~геометрии Лобачевского. Matematicheskoe Prosveshchenie, Matematicheskoe Prosveshchenie (2004), pp. 93-112. http://geodesic.mathdoc.fr/item/MP_2004_a9/
[1] James W. Andersen, Hyperbolic Geometry, Springer-Verlag, 1999 | MR
[2] C. I. Delman, G. Galperin, “A tale of three circles”, Mathematics Magazine, 76:1 (2003), 15–32