http://www.congreso.es/consti/constitucion/indice/titulos/articulos.jsp?ini=155&tipo=2
https://wiiw.ac.at/monthly-report-no-04-2024-dlp-6876.pdf
http://blogs.lse.ac.uk/brexit/2018/11/23/hubert-butler-essay-prize-what-happened-to-europe-without-frontiers/