United States. Bureau of Labor Statistics. "Coal," in United States. Bureau of Labor Statistics. "November 1988," PPI Detailed Report (November 1988) : 14-15. https://fraser.stlouisfed.org/title/63/item/21636/toc/53331 , accessed on April 19, 2024.
United States. Bureau of Labor Statistics. "Coal," in United States. Bureau of Labor Statistics. "November 1988," PPI Detailed Report (November 1988) : 14-15. https://fraser.stlouisfed.org/title/63/item/21636/toc/53331 , accessed on April 19, 2024.