@article{BUMI_1959_3_14_1_a7,
     author = {Hartman, Philip},
     title = {On oscillators with large frequencies.},
     journal = {Bollettino della Unione matematica italiana},
     pages = {62--65},
     publisher = {mathdoc},
     volume = {Ser. 3, 14},
     number = {1},
     year = {1959},
     zbl = {0086.07002},
     mrnumber = {104859},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/BUMI_1959_3_14_1_a7/}
}