#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int t;
  cin >> t;
  int m = 0, q = 0;
  for (int i = 0; i < t; i++) {
    char a;
    int a1, b1;
    cin >> a >> a1 >> b1;
    if (a == '+') {
      int s = (a1 > b1) ? a1 : b1;
      if (s > q) q = s;
      int s2 = (a1 < b1) ? a1 : b1;
      if (s2 > m) m = s2;
    } else {
      int f = (a1 > b1) ? a1 : b1;
      int s = (a1 < b1) ? a1 : b1;
      if (q <= f && m <= s)
        cout << "YES" << endl;
      else
        cout << "NO" << endl;
    }
  }
}
