P. Hejduková, L. Kureková, and M. Krechovská, “THE MEASUREMENT OF INDUSTRY 4.0: AN EMPIRICAL CLUSTER ANALYSIS FOR EU COUNTRIES”, Int. J. Econ. Sci., vol. 9, no. 1, pp. 121–134, Jun. 2020, doi: 10.20472/ES.2020.9.1.007.