https://energy.ec.europa.eu/system/files/2022-05/COM_2022_230_1_EN_ACT_part1_v5.pdf
https://www.scer.scot/wp-content/uploads/Future-of-Europe-Report-SCER-May-2019.pdf
https://taxfoundation.org/flat-tax-state-income-tax-reform/
https://ec.europa.eu/commission/sites/beta-political/files/outline_of_the_political_declaration.pdf