@article{TIMM_2009_15_4_a4,
     author = {V. I. Berdyshev},
     title = {Object visibility for a~group of observers with inaccurately given coordinates},
     journal = {Trudy Instituta matematiki i mehaniki},
     pages = {44--51},
     publisher = {mathdoc},
     volume = {15},
     number = {4},
     year = {2009},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TIMM_2009_15_4_a4/}
}