@book { Rechenschwierigkeitenvorbeugen,
    title = "Rechenschwierigkeiten vorbeugen",
    author = "Christina {Ostertag}",
    year = "2015",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    doi = "10.3726/978-3-653-05241-1",
    url = "https://www.peterlang.com/document/1048983"
}