@book { InvestinginCommodities,
    title = "Investing in Commodities",
    author = "Patrick {Maul}",
    year = "2011",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783842812857",
    url = "https://m.diplom.de/document/228446"
}