#include <bits/stdc++.h>
using namespace std;
bool mycompare(const tuple<int, int, int> &lhs,
               const tuple<int, int, int> &rhs) {
  return get<0>(lhs) < get<0>(rhs);
}
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  int n;
  cin >> n;
  int max_x = 0;
  int max_y = 0;
  int x, y;
  int h, w;
  char type;
  for (int i = 0; i < n; ++i) {
    cin >> type;
    if (type == '+') {
      cin >> x >> y;
      if (x > y) {
        swap(x, y);
      }
      max_x = max(x, max_x);
      max_y = max(y, max_y);
    } else {
      cin >> h >> w;
      if ((h >= max_x && w >= max_y) || (w >= max_x && h >= max_y)) {
        cout << "YES" << endl;
      } else {
        cout << "NO" << endl;
      }
    }
  }
  return 0;
}
