How to combine two not many?

Hello! In the study of sets, the question arose : How to combine two not many of this type(the left side)? d125afa8ce8144158b16b3b1b855b73e.PNG
How to cross the right part I know :
set<int> inter_no_AB;
 set_intersection(begin(universum_diff_A), end(universum_diff_A),
 begin(universum_diff_B), end(universum_diff_B),
 inserter(inter_no_AB, begin(inter_no_AB)));</int>

But at the expense of the left in difficulties. Tried to do by analogy, but there it was :
set<int> diff_union;
 set_union(begin(universum_diff_A), end(universum_diff_A),
 begin(universum_diff_B), end(universum_diff_B),
 inserter(diff_union, begin(diff_union)));</int>

This code snippet does not work properly.
Therefore, I ask Your help.
July 4th 19 at 23:05
1 answer
July 4th 19 at 23:07
If the original set given, something like this:

set<int> A_union_B;
set<int> diff_union;
 set_union(begin(A), end(A),
 begin(B) end(B),
 inserter(A_union_B, begin(A_union_B)));
 set_difference(begin(universum), end(universum),
 begin(A_union_B), end(A_union_B),
 inserter(diff_union, begin(diff_union)));</int></int>

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