@book { CleavageTheorie,
    title = "Cleavage-Theorie",
    author = "Björn {Siebert}",
    year = "2009",
    publisher = "GRIN Verlag",
    address = "München, Germany",
    doi = "10.3239/9783640243969",
    url = "https://www.hausarbeiten.de/document/121068"
}