@book { LebendigeGeometrie,
    title = "Lebendige Geometrie",
    subtitle = "Überlegungen zu einem integrativen Verständnis von Geometrieunterricht  anhand des Winkelbegriffes",
    author = "Konrad {Krainer}",
    year = "1990",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1077635"
}