@article{DANMA_2021_500_a17,
     author = {Yu. L. Sachkov and A. Yu. Popov},
     title = {Sub-Riemannian {Engel} sphere},
     journal = {Doklady Rossijskoj akademii nauk. Matematika, informatika, processy upravleni\^a},
     pages = {97--101},
     publisher = {mathdoc},
     volume = {500},
     year = {2021},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DANMA_2021_500_a17/}
}