https://www.socialeurope.eu/2017/07/time-eu-fair-movement-directive/
https://www.eurofound.europa.eu/sites/default/files/ef_publication/field_ef_document/ef1714en.pdf
http://library.fes.de/pdf-files/iez/13375.pdf
https://www.publications.parliament.uk/pa/ld201314/ldselect/ldeucom/164/164.pdf