#include <bits/stdc++.h>
using namespace std;
int main() {
  std ::ios ::sync_with_stdio(false);
  long long int n, mx = 0, mn = 0;
  cin >> n;
  char ch;
  long long int a, b;
  while (n--) {
    cin >> ch >> a >> b;
    if (ch == '+') {
      mx = max(mx, max(a, b));
      mn = max(mn, min(a, b));
    } else {
      if ((a >= mx && b >= mn) || (b >= mx && a >= mn)) {
        cout << "YES" << endl;
      } else
        cout << "NO" << endl;
    }
  }
  return 0;
}
