@book { StudienberdenVerfallderbulgarischenDeklination,
    title = "Studien über den Verfall der bulgarischen Deklination",
    subtitle = "Das bulgarische Kasussystem zu Beginn des 13. Jahrhunderts",
    author = "Klaus {Steinke}",
    year = "1968",
    publisher = "Biblion",
    address = ", Germany",
    doi = "10.3726/b12169",
    url = "https://www.peterlang.com/document/1067439"
}