#include <bits/stdc++.h>
using namespace std;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const long long int N = 200010;
signed main() {
  std::ios::sync_with_stdio(false);
  long long int q;
  cin >> q;
  long long int h = 0;
  long long int w = 0;
  while (q--) {
    char c;
    cin >> c;
    if (c == '+') {
      long long int x, y;
      cin >> x >> y;
      long long int t = min((long long int)x, (long long int)y);
      y = max((long long int)x, (long long int)y);
      x = t;
      h = max((long long int)h, (long long int)y);
      w = max((long long int)w, (long long int)x);
    } else {
      long long int x, y;
      cin >> x >> y;
      long long int t = min((long long int)x, (long long int)y);
      y = max((long long int)x, (long long int)y);
      x = t;
      if (h <= y && w <= x)
        cout << "YES"
             << "\n";
      else
        cout << "NO"
             << "\n";
    }
  }
}
