@article {1999,
	title = {Projection singularities of extremals for planar systems},
	number = {SISSA;90/99/M},
	year = {1999},
	publisher = {SISSA Library},
	url = {http://hdl.handle.net/1963/1304},
	author = {Ugo Boscain and Benedetto Piccoli}
}
