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@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/} }
Wintner, Aurel. On an instability criterion of Liapounoff. Portugaliae mathematica, Tome 15 (1956) no. 1, pp. 13-18. http://geodesic.mathdoc.fr/item/PORMA_1956__15_1_114763/