https://carnegieendowment.org/files/2-24_Lehne-EU_Geopolitics.pdf
http://cer.eu/in-the-press/speech-michel-barnier-future-eu-conference
http://www.cesifo-group.de/portal/page/portal/DocBase_Service/studien/Studie-2017-Felbermayr-etal-Brexit-79843.pdf