#include <bits/stdc++.h>
using namespace std;
int main() {
  cout << setprecision(20);
  ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);
  long long n;
  cin >> n;
  long long max_x = 0;
  long long max_y = 0;
  while (n--) {
    char t;
    long long x, y;
    cin >> t >> x >> y;
    if (x > y) swap(x, y);
    if (t == '+') {
      max_x = max(max_x, x);
      max_y = max(max_y, y);
    } else {
      cout << (max_x <= x && max_y <= y ? "YES" : "NO") << "\n";
    }
  }
  return 0;
}
