```c++ const std::vector<int> v1{1, 2, 5, 5, 5, 9}; const std::vector<int> v2{2, 5, 7}; std::vector<int> diff;
std::set_difference(v1.begin(), v1.end(), v2.begin(), v2.end(),
std::inserter(diff, diff.begin())); print(v1, "∖ "); print(v2, "= "); print(diff, "\n"); // yielding { 1 2 5 5 5 9 } ∖ { 2 5 7 } = { 1 5 5 9 } ```