https://www.foreignaffairs.com/europe/promise-and-peril-eu-expansion
https://ec.europa.eu/commission/sites/beta-political/files/revised_withdrawal_agreement_including_protocol_on_ireland_and_nothern_ireland.pdf
https://www.eurofound.europa.eu/sites/default/files/ef_publication/field_ef_document/ef1710en.pdf
https://ep00.epimg.net/descargables/2018/05/24/bfe9a6898e6b41480fd9d57aff93bc10.pdf