I'm going over my Discrete Structures assignment and an operator or something is used that I've never seen in the book or the notes. The questions is- Describe the following sets using the explicit method, withand then it gives sets A B C D and E explicitly, the questions im stuck on is - (C ? E) ? (A -(D ? B)) and B is complemented and D ? B is also complemented... what is that question mark, and what do I do with it??Code:U = {x|x E N ^ 1<x<10}