My answers. m.a. Bruno, Can you provide definitions of "belongs-to" and "included-in" that distinguish them from "union" and "intersection"?

Here we met a set of sets. The set of subsets of a set, can only be, of course, a set of sets. The set {2, 21, 14} is a set of numbers. The set { { }, {4, 78, 56} } is a set of sets. It has two elements: the empty set {}, and the set of numbers {4, 78, 56}. Do not confuse a number, like 24, and a set, like {24}, which is a set having a number has elements. In particular it is the case that {4, 78, 56} belongs to { { }, {4, 78, 56} }. Take it easy, and meditate on the following exercise: Which of the following are true {3, 5} included-in {3, 5} True {3, 5} belongs-to {3, 5} True {3, 5} included-in { {3, 5} } False {3, 5} belongs-to { {3, 5} } True Take your time, Bruno http://iridia.ulb.ac.be/~marchal/ --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Everything List" group. To post to this group, send email to everything-list@googlegroups.com To unsubscribe from this group, send email to everything-list+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/everything-list?hl=en -~----------~----~----~----~------~----~------~--~---