@article{ISU_2013_13_3_a5,
     author = {L. N. Romakina},
     title = {Hyperbolic parallelograms of the plane~$\widehat H$},
     journal = {Izvestiya of Saratov University. Mathematics. Mechanics. Informatics},
     pages = {43--52},
     publisher = {mathdoc},
     volume = {13},
     number = {3},
     year = {2013},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ISU_2013_13_3_a5/}
}