@book { DieProjektmethodenachFrey,
    title = "Die Projektmethode nach Frey",
    author = "Steffen {Rudolph}",
    year = "2012",
    publisher = "GRIN Verlag",
    address = "München, Germany",
    doi = "10.3239/9783656236245",
    url = "https://www.hausarbeiten.de/document/197469"
}