https://ec.europa.eu/info/sites/info/files/com-2018-890-final.pdf
https://publications.parliament.uk/pa/ld5801/ldselect/ldeucom/248/248.pdf
https://ec.europa.eu/commission/publications/terms-reference-article-50-treaty-european-union-negotiations_en
http://www.fdf.org.uk/news.aspx?article=7834