https://theconversation.com/ampliacion-o-profundizacion-de-la-union-europea-227125
https://www.europarl.europa.eu/doceo/document/B-9-2020-0098_EN.html?utm_source=POLITICO.EU&utm_campaign=3e49ba2509-EMAIL_CAMPAIGN_2020_02_13_05_53&utm_medium=email&utm_term=0_10959edeb5-3e49ba2509-190380769
https://www.lobbycontrol.de/wp-content/uploads/gaslobby-studie-lobbycontrol.pdf