
https://www.etui.org/sites/default/files/2022-01/22%20Social%20policy%20in%20the%20European%20Union.%20State%20of%20play%202021.%20Social%20ambitions%20EU%20pandemic_2022.pdf

http://www.cesifo-group.de/ifoHome/publications/working-papers/CESifoWP/CESifoWPdetails?wp_num=6441&CESifoWP.search=+

https://www.ipg-journal.de/regionen/global/artikel/detail/vorbei-mit-der-freiwilligkeit-4508/