https://library.fes.de/pdf-files/international/20258.pdf
https://www.nao.org.uk/wp-content/uploads/2017/07/The-Customs-Declaration-Service.pdf
https://www.merkur.de/politik/xi-jinping-putin-china-russland-energie-wirtschaftsforum-gas-oel-usbekistan-kasachstan-91947154.html