#include <bits/stdc++.h>
using namespace std;
const double pi = acos(-1.0);
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  int n;
  cin >> n;
  char x;
  int min, max;
  cin >> x >> min >> max;
  if (min > max) {
    swap(min, max);
  }
  for (int i = 0; i < n - 1; i += 1) {
    char y;
    int m, n;
    cin >> y >> m >> n;
    if (y == '+') {
      if (m > n) {
        swap(m, n);
      }
      if (m > min) {
        min = m;
      }
      if (n > max) {
        max = n;
      }
    } else {
      if (m > n) {
        swap(m, n);
      }
      if (m >= min && n >= max) {
        cout << "YES" << endl;
      } else {
        cout << "NO" << endl;
      }
    }
  }
}
