://www.open.ac.uk/conditions terms and conditions), this content is made available under a <a href="http://creativecommons.org/licenses/by-nc-sa/2No">http://creativecommons.org/licenses/by-nc-sa/2No</a> related items provided in this feed 3.1 Sets of sets In Section 2, all the sets and sequences we considered had primitive forms of data as their elements.