#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int t;
  cin >> t;
  int mn = -1, mx = -1;
  while (t--) {
    char c;
    int x, y;
    cin >> c >> x >> y;
    if (c == '+') {
      mn = max(mn, min(x, y));
      mx = max(mx, max(x, y));
    } else {
      if (mn <= min(x, y) && mx <= max(x, y))
        cout << "YES" << endl;
      else
        cout << "NO" << endl;
    }
  }
  return 0;
}
