https://www.boe.es/boe/dias/2021/12/30/pdfs/BOE-A-2021-21788.pdf
http://www.ftseglobalmarkets.com/news/uk-pension-deficits-rise-to-£145bn-liabilities-at-record-high.html
https://theconversation.com/the-gig-economy-is-nothing-new-it-was-standard-practice-in-the-18th-century-81057
https://opportunityinsights.org/wp-content/uploads/2020/05/tracker_paper.pdf