@book { Unternehmensrecht,
    title = "Unternehmensrecht",
    author = "Thomas {Tegen} and Adolf {Reul} and Andreas {Heidinger} and Jens {Tersteegen}",
    year = "2011",
    publisher = "Vahlen",
    address = "München, Deutschland",
    url = "https://vahlen.openpublishing.com/document/1220861"
}