https://www.ceps.eu/system/files/CEPS%20-%20LINKEDIN%20study%20FINAL.pdf
https://www.boeckler.de/data/downloads/IMK/FMM%20Konferenz%202023/v_2023_10_20_goekten.pdf
https://www.ipg-journal.de/regionen/global/artikel/detail/vorbei-mit-der-freiwilligkeit-4508/
http://sprc.info/wp-content/uploads/2012/07/Polish-Migrants-in-London-extending-the-stay.pdf