http://www.europarl.europa.eu/ftu/pdf/en/FTU_5.9.1.pdf
https://feps-europe.eu/wp-content/uploads/2023/11/PP23_WEB.pdf
https://www.propublica.org/article/how-private-nonprofits-ultrawealthy-tax-deductions-museums-foundation-art
https://www.nao.org.uk/wp-content/uploads/2018/01/PFI-and-PF2.pdf