@book{35620,
	author = {Costa, David G. and SpringerLink (Online service)},
	title = {An Invitation to Variational Methods in Differential Equations},
	publisher = {Birkhäuser Boston,},
	year = {2007.},
	address = {Boston, MA :},
	url = {http://dx.doi.org/10.1007/978-0-8176-4536-6}
}