@article{SEMR_2012_9_a13,
     author = {D. Yu. Sokolova},
     title = {On trapezoid area on the {Lobachevskii} plane},
     journal = {Sibirskie \`elektronnye matemati\v{c}eskie izvesti\^a},
     pages = {256--260},
     year = {2012},
     volume = {9},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/SEMR_2012_9_a13/}
}