@misc{Jonek-Kowalska_Izabela_Possibilities,
 author={Jonek-Kowalska, Izabela and Turek, Marian Czesław},
 howpublished={online},
 language={eng},
 title={Possibilities of improving the efficiency of mining companies by controlling cost of coal},
 keywords={koszty, efektywność, przedsiębiorstwo górnicze},
}