@book { InvestitionenunterUnsicherheit,
    title = "Investitionen unter Unsicherheit",
    author = "Friedrich {Petry}",
    year = "2001",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832438401",
    url = "https://m.diplom.de/document/219516"
}