If I could downvote this post, I would. This is a little bit like asking about the significance of the number 2. What you're asking is way too general. What ar

If I could downvote this post, I would. This is a little bit like asking about the significance of the number 2. What you're asking is way too general. What are we discussing? Maybe you can describe the contexts where you've seen this set and why you think it's surprising? Sets aren't usually studied in isolation.