#include <bits/stdc++.h>
using namespace std;
const int N = 5e5 + 5;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int t, mini = 1, maxi = 1;
  cin >> t;
  while (t--) {
    char ch;
    cin >> ch;
    if (ch == '+') {
      int x, y;
      cin >> x >> y;
      mini = max(mini, min(x, y));
      maxi = max(maxi, max(x, y));
    } else {
      int h, w;
      cin >> h >> w;
      if (h > w) swap(h, w);
      if (mini <= h && maxi <= w)
        cout << "YES" << endl;
      else
        cout << "NO" << endl;
    }
  }
  return 0;
}
