https://www.ipg-journal.de/regionen/global/artikel/detail/vorbei-mit-der-freiwilligkeit-4508/
http://www.ftseglobalmarkets.com/news/uk-pension-deficits-rise-to-£145bn-liabilities-at-record-high.html
https://www.wsi.de/fpdf/HBS-008657/p_wsi_report_86e_2023.pdf
https://www.adamsmith.org/adam-smith-lecture/