@book { BranchenanalyseHeizungsSanitrundLftungsbranche,
    title = "Branchenanalyse: Heizungs-, Sanitär- und Lüftungsbranche",
    author = "Adnan {Yalcin}",
    year = "2018",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    url = "https://m.diplom.de/document/455161"
}