@book { MusischesGymnasiumFrankfurtamMain19391945,
    title = "Musisches Gymnasium Frankfurt am Main 1939-1945",
    author = "Werner {Heldmann}",
    year = "2021",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1096410"
}