https://ec.europa.eu/commission/publications/agenda-19-june-meeting-between-eu-and-uk-article-50-negotiations_en
https://publications.parliament.uk/pa/cm201719/cmselect/cmpubacc/401/401.pdf
http://ukandeu.ac.uk/cancelling-brexit-what-would-happen-if-we-changed-our-mind-about-leaving-the-eu/