https://www.exact.com/benl/downloads/finance/whitepaper-cijfers-altijd-het-antwoord
https://www.nao.org.uk/wp-content/uploads/2018/01/PFI-and-PF2.pdf
https://www.boeckler.de/pdf/p_imk_report_125e_2017.pdf
https://www.ips-journal.eu/topics/economy-and-ecology/taking-the-fields-to-the-streets-7288/