@book { ZukunftsmarktSenioren,
    title = "Zukunftsmarkt Senioren",
    author = "Sandra {Engel}",
    year = "2001",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832434175",
    url = "https://m.diplom.de/document/219087"
}