@article{10_4153_S0008439519000456,
     author = {Zubelevic, Oleg},
     title = {On {Periodic} {Solutions} to {Constrained} {Lagrangian} {System}},
     journal = {Canadian mathematical bulletin},
     pages = {242--255},
     year = {2020},
     volume = {63},
     number = {1},
     doi = {10.4153/S0008439519000456},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/S0008439519000456/}
}