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https://pubs.aeaweb.org/doi/pdfplus/10.1257/jep.38.3.89
https://www.ippr.org/files/2018-03/cej-our-common-wealth-march2018.pdf
https://www.ecb.europa.eu/stats/accesstofinancesofenterprises/pdf/ecb.safe202005~c4b89a43b9.en.pdf