#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int n;
  cin >> n;
  long long H = 0, W = 0;
  while (n--) {
    char c;
    cin >> c;
    if (c == '+') {
      long long x, y;
      cin >> x >> y;
      if (max(H, x) * max(W, y) < max(W, x) * max(H, y)) {
        H = max(H, x);
        W = max(W, y);
      } else {
        H = max(H, y);
        W = max(W, x);
      }
    } else {
      long long h, w;
      cin >> h >> w;
      if ((H <= h && W <= w) || (H <= w && W <= h))
        cout << "YES" << endl;
      else
        cout << "NO" << endl;
    }
  }
  return 0;
}
