#include <bits/stdc++.h>
using namespace std;
const long long inf = 1e18;
const long double eps = 1e-6;
signed main() {
  ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);
  long long n;
  cin >> n;
  long long a = 0, b = 0;
  for (long long i = 0; i < n; ++i) {
    char c;
    cin >> c;
    if (c == '+') {
      long long ai, bi;
      cin >> ai >> bi;
      if (ai > bi) {
        swap(ai, bi);
      }
      a = max(a, ai);
      b = max(b, bi);
    } else {
      long long w, h;
      cin >> w >> h;
      if (w > h) {
        swap(w, h);
      }
      if (a <= w && b <= h) {
        cout << "YES\n";
      } else {
        cout << "NO\n";
      }
    }
  }
  return 0;
}
