@book { ZurProjektmethodenachKFrey, title = "Zur Projektmethode nach K. Frey", author = "Mareike {Müller}", year = "2011", publisher = "GRIN Verlag", address = "München, Germany", doi = "10.3239/9783656066019", url = "https://www.hausarbeiten.de/document/182713" }