Okay kiddo, let me explain what a credal set is. So, imagine you're playing a guessing game with your friends. You have to guess a number between 1 and 10. But, you're not quite sure what the number is, so you come up with a few guesses. Your guesses could be any number between 1 and 10.
Now, each guess you make is a possibility of what the number could be. This is called a "credal set." A credal set is basically a set of all possible guesses or beliefs that you have about something.
Let's say you guess that the number is either 3, 6, or 9. That's your credal set for this guessing game. These are the three possibilities that you think could be the right answer.
Now, as you play the game and your friends give you more clues, your credal set might change. Maybe your friends tell you that the number can only be odd. That means, you can remove the number 6 from your credal set since it's even. So, now your credal set is just 3 and 9.
In short, a credal set is a set of all possible beliefs or guesses that you have about something. As you learn more information or get more clues, your credal set might change.