@article{PIM_1952_S_S_IV_04_a12,
     author = {J. Popken},
     title = {An {Arithmetical} {Theorem} {Concerning} {Linear} {Differential} - {Difference} {Equations}},
     journal = {Publications de l'Institut Math\'ematique},
     pages = {121 },
     publisher = {mathdoc},
     volume = {_S_S_IV},
     number = {04},
     year = {1952},
     url = {http://geodesic.mathdoc.fr/item/PIM_1952_S_S_IV_04_a12/}
}