@book { LeistungspaketeimEigenheimbau,
    title = "Leistungspakete im Eigenheimbau",
    author = "Mathias {Schäfer}",
    year = "2021",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1107639"
}