@article{DAN_1979_249_3_a9,
     author = {V. P. Soltan and P. S. Soltan},
     title = {$d$-convex functions},
     journal = {Doklady Akademii Nauk},
     pages = {555--558},
     publisher = {mathdoc},
     volume = {249},
     number = {3},
     year = {1979},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1979_249_3_a9/}
}