#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int n, aa, x, y, w, h, mx = 0, my = 0;
  string s;
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> s >> x >> y;
    if (s == "+") {
      if (y > x) {
        aa = x;
        x = y;
        y = aa;
      }
      mx = max(mx, x);
      my = max(my, y);
    } else {
      if (y > x) {
        aa = x;
        x = y;
        y = aa;
      }
      if (mx <= x && my <= y) {
        cout << "YES" << endl;
      } else {
        cout << "NO" << endl;
      }
    }
  }
  return 0;
}
