#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  int n;
  cin >> n;
  int hm = 0, wm = 0;
  for (int i = 0; i < (int)(n); i++) {
    char c;
    int h, w;
    cin >> c >> h >> w;
    if (h < w) {
      swap(h, w);
    }
    if (c == '+') {
      hm = max(hm, h);
      wm = max(wm, w);
    } else {
      if (h >= hm && w >= wm) {
        cout << "YES" << endl;
      } else {
        cout << "NO" << endl;
      }
    }
  }
  return 0;
}
