@article{RM_1961_16_1_a18,
     author = {M. A. Akivis},
     title = {Transformations of surfaces by means of focal families of rays},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     publisher = {mathdoc},
     volume = {16},
     number = {1},
     year = {1961},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/RM_1961_16_1_a18/}
}