@book { SingenlehrenprivaterGesangsunterrichtheute,
    title = "Singen lehren - privater Gesangsunterricht heute",
    author = "Christiana {Jordan}",
    year = "2003",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832470777",
    url = "https://m.diplom.de/document/222396"
}