http://www.ips-journal.eu/regions/global/article/show/davos-2018-call-the-doctor-2544/
https://eur-lex.europa.eu/legal-content/FR/TXT/PDF/?uri=CELEX:32019L2121&from=EN
https://static.rusi.org/288_EI_Italy_Russia_China.pdf
https://taxfoundation.org/flat-tax-state-income-tax-reform/