@book { 110JahreWiedererrichtungdesbulgarischenStaates18781988,
    title = "110 Jahre Wiedererrichtung des bulgarischen Staates 1878-1988",
    author = "Klaus-Detlev {Grothusen}",
    year = "1990",
    publisher = "Biblion",
    address = ", Germany",
    doi = "10.3726/b12561",
    url = "https://www.peterlang.com/document/1067022"
}