@article{DM_1991_3_2_a10,
     author = {I. D. Kan},
     title = {M\"obius functions of the union of partial orders},
     journal = {Diskretnaya Matematika},
     pages = {121--127},
     publisher = {mathdoc},
     volume = {3},
     number = {2},
     year = {1991},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DM_1991_3_2_a10/}
}