@book { DieErweiterungenderG7,
    title = "Die Erweiterungen der G7",
    author = "Klaas {Schüller}",
    year = "2018",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    doi = "10.3726/b13404",
    url = "https://www.peterlang.com/document/1110616"
}