#include <bits/stdc++.h>
using namespace std;
using ll = int64_t;
const int N = 1e3 + 5;
int main() {
  ios_base ::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int q, mx = 0, my = 0;
  cin >> q;
  while (q-- > 0) {
    char type;
    int x, y;
    cin >> type >> x >> y;
    if (type == '+') {
      if (x > y) swap(x, y);
      mx = max(mx, x);
      my = max(my, y);
    } else {
      if ((mx <= x && my <= y) || (mx <= y && my <= x))
        cout << "YES" << '\n';
      else
        cout << "NO" << '\n';
    }
  }
  return 0;
}
