@article{SM_1972_16_1_a6,
     author = {V. G. Boltyanskii and P. S. Soltan},
     title = {Illumination from within of the boundary of a~convex body},
     journal = {Sbornik. Mathematics},
     pages = {87--94},
     year = {1972},
     volume = {16},
     number = {1},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1972_16_1_a6/}
}