@article{10_4064_am_12_4_391_395,
     author = {J. W\k{e}grzyn},
     title = {Differential equations with infinite number of limit cycles},
     journal = {Applicationes Mathematicae},
     pages = {391--395},
     publisher = {mathdoc},
     volume = {12},
     number = {4},
     year = {1971},
     doi = {10.4064/am-12-4-391-395},
     zbl = {0262.34019},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/am-12-4-391-395/}
}