@book { Frhaufklrungssysteme,
    title = "Frühaufklärungssysteme",
    author = "Veit {Aehlig}",
    year = "2002",
    publisher = "GRIN Verlag",
    address = "München, Germany",
    doi = "10.3239/9783638123136",
    url = "https://www.hausarbeiten.de/document/3733"
}