#include <iostream>
#include <set>
#include <string>
int main()
{
std::set<std::string> set={ "aaa", "bbb", "ccc", "ddd", "eee", "fff" };
size_t a = 1, b = 4;
for(auto it = std::next(set.begin(), a), it_end = std::next(it, b-a); it != it_end; ++it)
std::cout << *it << " ";
}
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