>> The point is that you can start with nothing, and define the set that has nothing in it. That's {}. Now we have one thing. We can define a set containing tha

>> The point is that you can start with nothing, and define the set that has nothing in it. That's {}. Now we have one thing. We can define a set containing that, so we have { {} }. Now we have two things, and we can definea set containing both of them, and so on. This helps a lot. I get it finally. :-) Thanks!