<ul><li><a href=http://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:12012E/TXT&from=EN target=_blank>Treaty on the Functioning of the European Union(Treaty on the Functioning of the European Union, Article 49, Title VI)</a></li><li><a href=https://eur-lex.europa.eu/legal-content/EN/TXT/?qid=1555406158601&uri=CELEX:02012L0034-20190101 target=_blank>Directive 2012/34/EU establishing a single European railway area(Directive 2012/34/EU of the European Parliament and of the Council of 21 November 2012 establishing a single European railway area. Last amended on the 14th of  Decembre 2016 by the Directive 2016/2370. )</a></li></ul>