@article{RM_1985_40_6_a11,
     author = {N. L. Koval'},
     title = {On upper and lower approximative liftings},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {129--130},
     publisher = {mathdoc},
     volume = {40},
     number = {6},
     year = {1985},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/RM_1985_40_6_a11/}
}