#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  ;
  int t;
  cin >> t;
  int l = 0;
  int r = 0;
  while (t--) {
    char c;
    cin >> c;
    if (c == '+') {
      int x, y;
      cin >> x >> y;
      l = max(l, min(x, y));
      r = max(r, max(x, y));
    } else {
      int h, w;
      cin >> h >> w;
      if (l <= min(h, w) and r <= max(h, w))
        cout << "YES" << endl;
      else
        cout << "NO" << endl;
    }
  }
  cerr << "Time : " << (double)clock() / (double)CLOCKS_PER_SEC << "s\n";
  return 0;
}
