@book { BeruflicheBeratunglterer,
    title = "Berufliche Beratung Älterer",
    author = "Bernd-Joachim {Ertelt} and Michael {Scharpf}",
    year = "2017",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    doi = "10.3726/b11357",
    url = "https://www.peterlang.com/document/1055321"
}