@article{AIHPA_1976__24_1_91_0,
     author = {Simon, Barry},
     title = {On the genericity of nonvanishing instability intervals in {Hills} equation},
     journal = {Annales de l'institut Henri Poincar\'e. Section A, Physique Th\'eorique},
     pages = {91--93},
     publisher = {Gauthier-Villars},
     volume = {24},
     number = {1},
     year = {1976},
     mrnumber = {473321},
     zbl = {0346.34015},
     language = {en},
     url = {http://www.numdam.org/item/AIHPA_1976__24_1_91_0/}
}