@article{VMUMM_1989_4_a12,
     author = {G. M. Vinner},
     title = {Stability of the equilibrium of a mechanical system with unilateral constraints},
     journal = {Vestnik Moskovskogo universiteta. Matematika, mehanika},
     pages = {54--57},
     year = {1989},
     number = {4},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/VMUMM_1989_4_a12/}
}