foo.cc: In function ‘int main()’:
foo.cc:23:25: error: ‘class std::priority_queue<int>’ has no member named ‘front’
   23 |                 if (app.front() >= tt.front()) {
      |                         ^~~~~
foo.cc:23:39: error: ‘class std::priority_queue<int>’ has no member named ‘front’
   23 |                 if (app.front() >= tt.front()) {
      |                                       ^~~~~
foo.cc:25:29: error: ‘class std::priority_queue<int>’ has no member named ‘pop_front’
   25 |                         app.pop_front();
      |                             ^~~~~~~~~
foo.cc:26:28: error: ‘class std::priority_queue<int>’ has no member named ‘pop_front’
   26 |                         tt.pop_front();
      |                            ^~~~~~~~~
foo.cc:29:28: error: ‘class std::priority_queue<int>’ has no member named ‘pop_front’
   29 |                         tt.pop_front();
      |                            ^~~~~~~~~