@article {journals/ipl/ManolopoulosV91,
	title = {Seek Distances in Disks with Two Independent Heads Per Surface},
	journal = {Inf. Process. Lett.},
	volume = {37},
	number = {1},
	year = {1991},
	pages = {37-42},
	author = {Manolopoulos, Yannis and Athena Vakali}
}