@book{21811,
	author = {Enochs, Edgar E. and Jenda, Overtoun M.G.},
	title = {Relative homological algebra; volume1},
	publisher = {Walter de Gruyter},
	year = {2011},
	series = {de Gruyter expositions in mathematics; 30},
	address = {Berlin},
	edition = {2nd ed.}
}