@article{MAN_1970__189_162068,
     author = {G. FRANK and J. NIKOLAUS},
     title = {Zum {Umkehrproblem} f\"ur lineare {Differentialgleichungen} mit {Polynomen} als {Koeffizienten.}},
     journal = {Mathematische Annalen},
     pages = {169--177},
     publisher = {mathdoc},
     volume = {189},
     year = {1970},
     zbl = {0204.39902},
     url = {http://geodesic.mathdoc.fr/item/MAN_1970__189_162068/}
}