https://www.ipg-journal.de/regionen/global/artikel/detail/vorbei-mit-der-freiwilligkeit-4508/
https://www.boeckler.de/pdf/p_imk_report_141e_2018.pdf
https://www.adamsmith.org/adam-smith-lecture/
https://www.tuc.org.uk/sites/default/files/Brexit%20Legal%20Opinion.pdf