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Date: 2011-09-13 09:28:47		This article was downloaded by: [University of Porto] On: 12 September 2011, At: 03:32 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: Registered office: Mortimer House, Add to Reading List Source URL: www.math.udel.edu Download Document from Source Website File Size: 833,52 KB Share Document on Facebook