@article{JMPA_1935_9_14_1-4_49_0,
     author = {Morse, Marston},
     title = {Instability and transitivity},
     journal = {Journal de Math\'ematiques Pures et Appliqu\'ees},
     pages = {49--71},
     publisher = {Gauthier-Villars},
     volume = {Ser. 9, 14},
     number = {1-4},
     year = {1935},
     zbl = {0011.13104},
     language = {en},
     url = {http://archive.numdam.org/item/JMPA_1935_9_14_1-4_49_0/}
}