@article{DM_1989_1_1_a7,
     author = {A. A. Sapozhenko},
     title = {The number of antichains in ranked partially ordered sets},
     journal = {Diskretnaya Matematika},
     pages = {35--58},
     publisher = {mathdoc},
     volume = {1},
     number = {1},
     year = {1989},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DM_1989_1_1_a7/}
}