#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  int n;
  cin >> n;
  int bx = 0, by = 0;
  while (n--) {
    char c;
    cin >> c;
    if (c == '+') {
      int x, y;
      cin >> x >> y;
      bx = max(bx, max(x, y));
      by = max(by, min(x, y));
    } else {
      int h, w;
      cin >> h >> w;
      if (max(h, w) >= bx && min(h, w) >= by) {
        cout << "YES";
      } else {
        cout << "NO";
      }
      cout << endl;
    }
  }
}
