#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int MAX = 1e5;
void solve() {
  int n;
  cin >> n;
  int mx = 0, my = 0;
  while (n--) {
    char t;
    cin >> t;
    if (t == '+') {
      int x, y;
      cin >> x >> y;
      if (x > y) {
        swap(x, y);
      }
      mx = max(mx, x);
      my = max(my, y);
    } else {
      int h, w;
      cin >> h >> w;
      if (h > w) {
        swap(h, w);
      }
      if (mx <= h && my <= w) {
        cout << "YES\n";
      } else {
        cout << "NO\n";
      }
    }
  }
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  solve();
  return 0;
}
