@article{CourantEtAl:1928:MathAnnalen:100:32,
	author		= "Courant , R. and Friedrichs , K. and Lewy ,
                           H.", 
	year		= "1928",
	title		= "Uber die partiellen Differenzengleichungen
                           der mathematischen Physik", 
	journal		= "Math. Annalen",
	volume		= "100",
	pages		= "32--74"}
