@book{heuser,
    author = {Heuser, Harro},
    title = {Gew{\"o}hnliche Differentialgleichungen},
    subtitle = {Einf{\"u}hrung in Lehre und Gebrauch},
    publisher = {Vieweg+Teubner Verlag},
    year = {2009},
    edition = {6},
    pages = {453,460,462},
}

@book{grune,
    author = {Gr{\"u}ne, Lars AND Junge, Oliver},
    title = {Gew{\"o}hnliche Differentialgleichungen},
    subtitle = {Eine Einführung aus der Perspektive der dynamischen Systeme},
    publisher = {Vieweg+Teubner Verlag},
    year = {2009},
    pages = {10--16},
}