@article{RSMUP_1987__77__193_0,
     author = {Marzantowicz, Wac{\l}aw and Parusi\'nski, Adam},
     title = {Periodic solutions near an equilibrium of a differential equation with a first integral},
     journal = {Rendiconti del Seminario Matematico della Universit\`a di Padova},
     pages = {193--206},
     publisher = {Seminario Matematico of the University of Padua},
     volume = {77},
     year = {1987},
     zbl = {0651.34040},
     language = {en},
     url = {http://archive.numdam.org/item/RSMUP_1987__77__193_0/}
}