https://www.socialeurope.eu/the-german-debt-brake-reform-urgent
http://cep.lse.ac.uk/pubs/download/brexit11.pdf
https://www.suerf.org/docx/f_ec43638b66e16a5bbede9b710b12b0c7_32333_suerf.pdf
https://www.cesifo-group.de/DocDL/EEAG-2018.pdf