Yegorova-Gudkova, T., M. Bojko, Y. Neustroiev, O. Khostash, L. Pan, H. Shepitko, V. Beloborodko, O. Zvirkov, M. Kirilina, and I. Matjukhina. “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, vol. 4, no. 4(60), July 2021, pp. 41-45, doi:10.15587/2706-5448.2021.239035.