JONEK-KOWALSKA, Izabela and TUREK, Marian. Possibilities of Improving the Efficiency of Mining Companies. Equilibrium. Equilibrium. Quarterly Journal of Economics and Economic Policy. Online. 14 March 2011. Vol. 6, no. 2, pp. 91-108. [Accessed 7 July 2025]. DOI 10.12775/EQUIL2011.014.