@article{ARM_1978_14_3_a1,
     author = {Guggenheimer, H.},
     title = {On focal points and limit behavior of solutions of linear differential equations},
     journal = {Archivum mathematicum},
     pages = {139--143},
     year = {1978},
     volume = {14},
     number = {3},
     mrnumber = {0508430},
     zbl = {0403.34027},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/ARM_1978_14_3_a1/}
}