http://www.case-research.eu/files/?id_plik=5223
https://ukandeu.ac.uk/how-europe-can-avoid-a-second-lockdown/
https://www.dbresearch.de/PROD/RPS_DE-PROD/PROD0000000000523908/Deutschland%3A_Konjunktur_kurzgefasst.PDF
https://www.brookings.edu/blog/future-development/2018/04/03/the-middle-productivity-trap-why-are-less-productive-firms-systematically-lagging-behind/?utm_campaign=Brookings%20Brief&utm_source=hs_email&utm_medium=email&utm_content=61867197