vector<int> v = {9, 2, 5, 1};
     auto isEven = [](const int& a){ return a % 2 == 0; };
     cout << (all_of(v.begin(), v.end(), isEven) ? "Yes\n" : "No\n"); //outputs: No
     v = {2, 4, 6};
     cout << (all_of(v.begin(), v.end(), isEven) ? "Yes\n" : "No\n"); // outputs: YES