#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base ::sync_with_stdio(false);
  int Q, a, b, x = 0, y = 0;
  string st;
  cin >> Q;
  while (Q--) {
    cin >> st >> a >> b;
    if (a > b) {
      swap(a, b);
    }
    if (st == "+") {
      x = max(x, a), y = max(y, b);
    } else {
      if (a >= x && b >= y) {
        cout << "YES\n";
      } else {
        cout << "NO\n";
      }
    }
  }
}
