https://www.esri.ie/system/files/publications/RS185_0.pdf
https://www.migrationpolicy.org/article/spain-immigration-system-evolution?eType=EmailBlastContent&eId=a1fcdaaa-93ef-4a35-9397-e325534c6592&mc_cid=e4eef57c9d&mc_eid=d10a99d01e
https://www.gov.uk/guidance/status-of-eu-nationals-in-the-uk-what-you-need-to-know
http://www.resolutionfoundation.org/app/uploads/2018/02/IC-international.pdf