@article{FPM_2009_15_1_a6,
     author = {M. A. Pervukhin and A. A. Stepanova},
     title = {Axiomatizability of free $S$-posets},
     journal = {Fundamentalʹna\^a i prikladna\^a matematika},
     pages = {99--115},
     publisher = {mathdoc},
     volume = {15},
     number = {1},
     year = {2009},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/FPM_2009_15_1_a6/}
}