Description: The value of a finite set of sequential integers. E.g., 2 ... 5
means the set { 2 , 3 , 4 , 5 } . A special case of this definition
(starting at 1) appears as Definition 11-2.1 of Gleason p. 141, where
NN_k means our 1 ... k ; he calls these setssegments of the
integers. (Contributed by NM, 6-Sep-2005)(Revised by Mario Carneiro, 3-Nov-2013)