Canh, N. P., S. D. Thanh, C. Schinckus, J. Bensemann, and L. T. Thanh. “Global Emissions: A New Contribution from the Shadow Economy”. International Journal of Energy Economics and Policy, vol. 9, no. 3, Apr. 2019, pp. 320-37, https://www.econjournals.com/index.php/ijeep/article/view/7244.