@book { Mobilityconceptsandtourismtravel,
    title = "Mobility concepts and tourism travel",
    author = "Ginka {Tchervenkova}",
    year = "2005",
    publisher = "GRIN Verlag",
    address = "München, Germany",
    doi = "10.3239/9783638442169",
    url = "https://www.hausarbeiten.de/document/47221"
}