https://www.euronews.com/2018/09/25/why-is-the-irish-border-issue-so-complex-euronews-answers
https://ec.europa.eu/commission/publications/position-paper-transmitted-eu27-governance_en
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/728135/THE_FUTURE_UK-EU_RELATIONSHIP.pdf
https://publications.parliament.uk/pa/cm201719/cmselect/cmpubacc/401/401.pdf