@book { GrammatikdesJopara,
    title = "Grammatik des «Jopara»",
    subtitle = "Gesprochenes Guaraní und Spanisch in Paraguay",
    author = "Guido {Kallfell}",
    year = "2011",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1108246"
}