Voir la notice de l'article provenant de la source European Digital Mathematics Library
@article{MS_1970__124_2_a5, author = {{\CYRS}.{\CYRP}. {\CYRG}{\cyre}{\cyrishrt}{\cyrs}{\cyrb}{\cyre}{\cyrr}{\cyrg}}, title = {{\CYRO} {\cyrs}{\cyrv}{\cyro}{\cyrishrt}{\cyrs}{\cyrt}{\cyrv}{\cyra}{\cyrh} {\cyrn}{\cyro}{\cyrr}{\cyrm}{\cyra}{\cyrl}{\cyrsftsn}{\cyrn}{\cyro}{\cyrg}{\cyro} {\cyro}{\cyrt}{\cyro}{\cyrb}{\cyrr}{\cyra}{\cyrzh}{\cyre}{\cyrn}{\cyri}{\cyrya}, {\cyrp}{\cyro}{\cyrr}{\cyro}{\cyrzh}{\cyrd}{\cyra}{\cyre}{\cyrm}{\cyro}{\cyrg}{\cyro} {\cyru}{\cyrr}{\cyra}{\cyrv}{\cyrn}{\cyre}{\cyrn}{\cyri}{\cyre}{\cyrm} $rt-s^2 = -f^2(x,y)$}, journal = {Matemati\v{c}eskij sbornik}, pages = {224--232}, publisher = {mathdoc}, volume = {124}, number = {2}, year = {1970}, zbl = {0194.52501}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/MS_1970__124_2_a5/} }
С.П. Гейсберг. О свойствах нормального отображения, порождаемого уравнением $rt-s^2 = -f^2(x,y)$. Matematičeskij sbornik, Tome 124 (1970) no. 2, pp. 224-232. http://geodesic.mathdoc.fr/item/MS_1970__124_2_a5/