@book{184994,
	author = {United Nations.},
	title = {International classification of hard coals by type /},
	publisher = {United Nations,},
	year = {1956.},
	series = {[United Nations. Document] E/ECE/247, E/ECE/Coal/110},
	address = {Geneva :},
	note = {"United Nations publication. Sales no. : 1956.II.E.4."}
}