#include <bits/stdc++.h>
using namespace std;
int main() {
  long long q, x, y, max_x = 0, max_y = 0, i, h, w;
  char c;
  scanf("%lld", &q);
  while (q--) {
    cin >> c;
    scanf("%lld%lld", &x, &y);
    h = max(x, y);
    w = min(x, y);
    if (c == '+') {
      max_x = max(h, max_x);
      max_y = max(max_y, w);
    } else {
      if ((max_x <= h && max_y <= w)) {
        cout << "YES" << endl;
      } else {
        cout << "NO" << endl;
      }
    }
  }
}
