some one can help me please and explain to me how to prove this:
Thank you very much!
I ready don't know to go to it...
You posted the question. Therefore, you should know what the symbols mean. Frankly, I do not know what means in this context. I guess it probably means the set complement.
That is why you have text material. The identity is still correct.
For every set it is the case that . It is true .