Regular closed set

A regular closed set is a place where you can put things and they won't get away. Imagine you have a bunch of toys and you don't want them to escape. You put them in a box with a lid on it, and that box becomes a regular closed set. The toys are inside and they can't get out because the box is closed.

A regular closed set is like this box. It's a special place where we can put things and they won't be able to get away because the place is closed. The set is called "regular" because it follows some special rules about how it's closed.

Think about a zoo with different animal exhibits. Each exhibit is a separate regular closed set. The animals are all inside and can't get out because the exhibit is closed. The zookeepers have to follow special rules to make sure the exhibits are regular and that the animals stay safe inside.

So, in summary, a regular closed set is like a box or a zoo exhibit that is closed and follows special rules to keep things inside. It's a way for mathematicians to describe a special type of set.