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)));
Math.abs(a-b)/(a-b)