#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  int maxim1 = 0, maxim2 = 0;
  int q;
  cin >> q;
  while (q--) {
    char c;
    int x, y;
    cin >> c >> x >> y;
    if (c == '+') {
      maxim1 = max(maxim1, min(x, y));
      maxim2 = max(maxim2, max(x, y));
    } else if (maxim1 <= min(x, y) && maxim2 <= max(x, y))
      cout << "YES" << endl;
    else
      cout << "NO" << endl;
  }
  return 0;
}
