#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);
  srand(time(NULL));
  int n;
  cin >> n;
  int max_a = 0, max_b = 0;
  ;
  while (n--) {
    char c;
    int x, y;
    cin >> c >> x >> y;
    if (x > y) {
      swap(x, y);
    }
    if (c == '?') {
      if (x >= max_a && y >= max_b) {
        cout << "YES\n";
      } else {
        cout << "NO\n";
      }
    } else {
      max_a = max(max_a, x);
      max_b = max(max_b, y);
    }
  }
}
