@article{DAN_1989_304_5_a4,
     author = {M. I. Zelikin and V. F. Borisov},
     title = {Fields of optimal trajectories that contain second-order singular},
     journal = {Doklady Akademii Nauk},
     pages = {1050--1053},
     publisher = {mathdoc},
     volume = {304},
     number = {5},
     year = {1989},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1989_304_5_a4/}
}