https://single-market-economy.ec.europa.eu/system/files/2023-03/Study%202023%20CRM%20Assessment.pdf
http://openeurope.org.uk/today/blog/will-brexit-ground-flights-europe/
https://www.bertelsmann-stiftung.de/fileadmin/files/BSt/Publikationen/GrauePublikationen/WKIO_2020_final.pdf?utm_source=POLITICO.EU&utm_campaign=15a7cc1e87-EMAIL_CAMPAIGN_2020_04_08_08_59&utm_medium=email&utm_term=0_10959edeb5-15a7cc1e87-190380769
https://rhg.com/wp-content/uploads/2022/03/RHG-US-Policy-to-Reduce-Russian-Energy-Leverage.pdf