@article{CMFD_2011_42_a3,
     author = {A. A. Ardentov},
     title = {Extremal paths in the nilpotent {sub-Riemannian} problem on the {Engel} group (subcritical case of pendulum oscillations)},
     journal = {Contemporary Mathematics. Fundamental Directions},
     pages = {30--35},
     publisher = {mathdoc},
     volume = {42},
     year = {2011},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/CMFD_2011_42_a3/}
}