#include <bits/stdc++.h>
using namespace std;
int main() {
  std::ios::sync_with_stdio(false);
  int q;
  cin >> q;
  long long mn = 0;
  long long mx = 0;
  for (int i = 0; i < q; i++) {
    char c;
    cin >> c;
    long long a, b;
    cin >> a >> b;
    if (a > b) swap(a, b);
    if (c == '+') {
      mn = max(mn, a);
      mx = max(mx, b);
    } else {
      if (mn <= a && mx <= b) {
        cout << "YES" << endl;
      } else {
        cout << "NO" << endl;
      }
    }
  }
  int pause;
  cin >> pause;
  return 0;
}
