https://www.progressivepolicy.org/blogs/trade-fact-of-the-week-americas-non-mfn-tariffs-on-natural-resources-are-usually-low/
https://ec.europa.eu/commission/sites/beta-political/files/customs_controls_0.pdf
https://www.project-syndicate.org/commentary/g20-solutions-to-ending-inequality-by-helle-thorning-schmidt-2017-07