@book{178869,
	author = {Economic Commission for Europe.   },
	title = {Concentration of collieryworkings inselected European countries /},
	publisher = {United Nations,},
	year = {1961.},
	series = {series F. no. 21 },
	address = {Geneva :},
	note = {"National accounts statistics, series X, no. 18, speical issue."}
}