#include <bits/stdc++.h>
using namespace std;
int main() {
  cin.tie(0);
  cout.sync_with_stdio(false);
  long long n;
  cin >> n;
  long long x = 0, y = 0;
  for (long long i = 0; i < n; i++) {
    char c;
    long long a, b;
    cin >> c;
    cin >> a >> b;
    if (a < b) swap(a, b);
    if (c == '+') {
      x = max(x, a);
      y = max(y, b);
    } else {
      if (x <= a && y <= b) {
        cout << "YES\n";
      } else
        cout << "NO\n";
    }
  }
  return 0;
}
