Yegorova-Gudkova, T., Bojko, M., Neustroiev, Y., Khostash, O., Pan, L., Shepitko, H., Beloborodko, V., Zvirkov, O., Kirilina, M. and Matjukhina, I. 2021. Development of an innovative methodology of research of systems on an example of a shadow economy as an invariant of system of economic security of state. Technology audit and production reserves. 4, 4(60) (Jul. 2021), 41–45. DOI:https://doi.org/10.15587/2706-5448.2021.239035.