@book { EinfachAllesMerken,
    title = "Einfach. Alles. Merken.",
    subtitle = "Das perfekte Gedächtnistraining. Geniale Merktechniken",
    author = "Ulrich {Bien}",
    year = "2021",
    publisher = "humboldt",
    address = "Hannover, Deutschland",
    url = "https://schluetersche.openpublishing.com/document/1153440"
}