@book { NiklasLuhmannunddieSystemtheorie,
    title = "Niklas Luhmann und die Systemtheorie",
    author = "Roman {Behrens}",
    year = "2010",
    publisher = "GRIN Verlag",
    address = "München, Germany",
    doi = "10.3239/9783640762651",
    url = "https://www.hausarbeiten.de/document/156582"
}