On Feb 4, 2010, at 12:37 AM, Duane Nickull wrote:
Can you please clarify what you mean by “Sets are timeless; they cannot change their members”. Do you mean they cannot add new members? Can they not change enumeration lists of existing members? Can existing members values be retracted?
A set is defined as a collection of things, in an abstract sense of 'collection'. It is defined by its members or elements: if A has the same members as B, and A and B are sets then A *is* B. There isn't anything to a set other than the members it has; it has no 'identity' beyond being the set of things that it is a set of. A set is not a separate 'thing' with a state that can be updated or changed. It is not a data structure. So, to answer your questions: no, a set cannot add new members. First, the idea of a set doing anything (like 'adding" ) doesn't make sense; but even if it did, adding something to a set makes a new set, one that is different from the first set. Sets cannot change their lists (they don't have lists, anyway) and members cannot be retracted: if you 'take something out of' a set, then you have a different set.