@book { TelefonwerbunginDeutschland,
    title = "Telefonwerbung in Deutschland",
    author = "Anca {David}",
    year = "2019",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    doi = "10.3726/b14919",
    url = "https://www.peterlang.com/document/1110688"
}