Normally what I know is that you can make a union or an intersection between 2 sets. In this expression Its a big union of a set. I'm asking about the meaning of such expression, What does it mean. What is the infinity sign means being at the top?
Things got even more complicated with seeing De Morgan's Law:
Which uses the same expression of big U?
Anyone who can explain to me the expression or De Morgan's Laws would be much appreciated. Thanks