@book { ThemamitVariationen,
    title = "Thema mit Variationen",
    author = "Ahti {Jäntti} and Jarkko {Nurminen}",
    year = "2021",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1098389"
}