@article{MZM_1968_3_4_a4,
     author = {G. A. Kovaleva},
     title = {Example of a~surface that is homotopic to a~tube and has a~closed asymptotic line},
     journal = {Matemati\v{c}eskie zametki},
     pages = {403--413},
     publisher = {mathdoc},
     volume = {3},
     number = {4},
     year = {1968},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1968_3_4_a4/}
}