@article{PORMA_1956__15_1_114763,
     author = {Wintner, Aurel},
     title = {On an instability criterion of {Liapounoff}},
     journal = {Portugaliae mathematica},
     pages = {13--18},
     publisher = {mathdoc},
     volume = {15},
     number = {1},
     year = {1956},
     mrnumber = {0082019},
     zbl = {0071.30802},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PORMA_1956__15_1_114763/}
}