United States. Bureau of Labor Statistics. "Coal," in United States. Bureau of Labor Statistics. "December 1985," PPI Detailed Report (December 1985) : 17-18. https://fraser.stlouisfed.org/title/63/item/21601/toc/408457 , accessed on April 25, 2024.
United States. Bureau of Labor Statistics. "Coal," in United States. Bureau of Labor Statistics. "December 1985," PPI Detailed Report (December 1985) : 17-18. https://fraser.stlouisfed.org/title/63/item/21601/toc/408457 , accessed on April 25, 2024.