Hey guys. To introduce myself to the forum, I'm a first (going on second) year Computer Science student from Liverpool UK. Just a quick question on a symbol I have come across;

I know the union of sets, $\displaystyle A \cup B$ joins all elements in A and B. As far as I can tell from the description it is the union of all the sets $\displaystyle $A_{x}$$ where $\displaystyle x$ is an element of $\displaystyle X$. The lines being the cardinality of this set which has been joined (union).

Am I close at all to it's meaning? If so, could you then have a big intersect symbol to intersect the sets produced. There is also an example later with $\displaystyle b \in C$ under the big union symbol, is this just a condition for the union operation?