@book { WandeldesdeutschenParteiensystems,
    title = "Wandel des deutschen Parteiensystems",
    author = "Marcus {Sommer}",
    year = "2008",
    publisher = "GRIN Verlag",
    address = "München, Germany",
    doi = "10.3239/9783640135523",
    url = "https://www.hausarbeiten.de/document/113175"
}