https://www.diw.de/documents/publikationen/73/diw_01.c.578096.de/18-7-3.pdf
https://www.socialeurope.eu/progressive-taxation-for-a-renewed-social-contract
https://think.ing.com/articles/four-scenarios-for-eurozone-reform-at-this-weeks-eu-summit/
http://www.case-research.eu/files/?id_plik=5223