@book { Sales,
    title = "Sales!",
    subtitle = "11 Erfolgsfaktoren im B2B-Vertrieb",
    author = "Hartmut {Sieck} and Andreas {Goldmann}",
    year = "2017",
    publisher = "Vahlen",
    address = "München, Deutschland",
    url = "https://vahlen.openpublishing.com/document/1217959"
}