@book{134908,
	author = {Bobylev, N. A. and Burman, Yu. M.},
	title = {Approximation procedures in nonlinear oscillation theory /},
	publisher = {W. de Gruyer,},
	year = {1994.},
	address = {Berlin ;},
	url = {http://site.ebrary.com/lib/rucke/Doc?id=10782139}
}