Borówka , Borys. 2009. "Classification and Protection of Hard Coal Deposit Resources in Poland". Записки Горного института 181 (март), 14-16. https://pmi.spmi.ru/pmi/article/view/7012.

Borówka , Borys. 2009. "Classification and Protection of Hard Coal Deposit Resources in Poland". Journal of Mining Institute 181 (March), 14-16. https://pmi.spmi.ru/pmi/article/view/7012.