@book { OKR,
    title = "OKR",
    author = "John {Doerr} and Klaus {Möller} and Tobias {Flinspach} and Stefano L. {Saeger}",
    year = "2018",
    publisher = "Vahlen",
    address = "München, Deutschland",
    url = "https://vahlen.openpublishing.com/document/1219103"
}