#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  int n, d = 0, e = 0;
  cin >> n;
  for (int i = 0; i < n; i++) {
    char a;
    int b, c;
    cin >> a >> b >> c;
    if (a == '+') {
      d = b > c ? (b > d ? b : d) : (c > d ? c : d);
      e = b > c ? (c > e ? c : e) : (b > e ? b : e);
    } else {
      if (((d <= b) && (e <= c)) || ((d <= c) && (e <= b)))
        cout << "YES";
      else
        cout << "NO";
    }
    cout << endl;
  }
}
