JONEK-KOWALSKA, Izabela; TUREK, Marian. Possibilities of Improving the Efficiency of Mining Companies. Equilibrium. Quarterly Journal of Economics and Economic Policy, Olsztyn, v. 6, n. 2, p. 91–108, 2011. DOI: 10.12775/EQUIL2011.014. Disponível em: https://economic-policy.pl/index.php/eq/article/view/410. Acesso em: 8 feb. 2026.