@article {1293,
	title = {Curves that must be retraced},
	journal = {Information and Computation},
	volume = {209},
	year = {2011},
	pages = { 992--1006},
	url = {http://webdiis.unizar.es/~elvira/research.html},
	author = {X. Gu and J.H. Lutz and E. Mayordomo}
}

