#include <algorithm>
#include <iterator>
#include <iostream>

int main()
{
  double a[] = { 2, 4, 6, 8 };
  double b[] = { 2, 3, 5, 7 };

  std::set_union(a, a+4, b, b+4, std::ostream_iterator<double>(std::cout, " "));
}