@article {FeLuMaRe05,
	title = {Weakly useful sequences},
	journal = {Information and Computation},
	volume = {197},
	year = {2005},
	pages = {41-54},
	url = {http://webdiis.unizar.es/\%7Eelvira/publicaciones/wus.pdf},
	author = {S.A. Fenner and J.H. Lutz and E. Mayordomo and P. Reardon}
}

