@misc{Jonek-Kowalska_Izabela_Cost,
 author={Jonek-Kowalska, Izabela},
 howpublished={online},
 language={eng},
 title={Cost analysis and assessment in the Polish hard coal mining industry in years 2006-2011},
 keywords={analiza kosztów, ocena kosztów, górnictwo węgla kamiennego, Polska},
}