https://ec.europa.eu/commission/sites/beta-political/files/guiding-principles-dialogue-ei-ni_en.pdf
https://ec.europa.eu/commission/publications/position-paper-essential-principles-citizens-rights_en
http://www.conservativehome.com/thecolumnists/2017/05/christopher-howarths-guide-to-brexit-the-manifesto-must-convince-leavers-and-lock-in-our-escape-from-the-eu.html
http://www.europarl.europa.eu/cmsdata/115748/IPOL_IDA(2017)583130_EN.pdf