Calculating Strange Union Hello everyone assume that we set $A$ = {{1 ,2} , {2 ,3} ,{4 ,3}}
so what is $\cup_{B \in A} (B)$?
 A: $\{1,2\}\cup \{2,3\} \cup \{4,3\}$..
A: Here The elements of $A$ are $\{1,2\}, \{2,3\}, \{4,3\}$. So the union of elements of $A$ is:
$$\cup_{B\in A} B = \{1,2\} \cup \{2,3\} \cup \{4,3\}.$$
A: I surmise that this was a trick question.  The intention is for the student to realize that the union of all elements of a specific set is the specific set itself, without any regard to what the elements actually are.
Addendum
Subsequent comments by Aurelio and Coward have suggested that I am mistaken.
I may well be mistaken, but I'm just not seeing it yet.
Coward: In response to your comment, could you please provide a counter example?
Aurelio: In response to your counter example, perhaps I'm missing something here.
In your counter example, it does seem to me that $\bigcup_{b \in A} \;=\; A.$
Please explain if you think that I am mistaken.
Addendum-2
In response to John Hughes comment below:
Well this is an eye-opener.  His explanation, which never occurred to me, does seem sensible.
I now have to say that (apparently) my knowledge of set theory (re interpretation of notation) is deficient, so my answer (above) may well be wrong.
