@book { BulgarienJahrbuch2011,
    title = "Bulgarien-Jahrbuch 2011",
    author = "Sigrun {Comati} and Helmut {Schaller} and Wolfgang {Gesemann} and Raiko {Krauß}",
    year = "2012",
    publisher = "Biblion",
    address = ", Germany",
    doi = "10.3726/b12812",
    url = "https://www.peterlang.com/document/1067457"
}