#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long t, i, j, l = 0, b = 0, x, y;
  cin >> t;
  while (t--) {
    char c;
    cin >> c >> x >> y;
    if (c == '+') {
      b = max(min(x, y), b);
      l = max(max(x, y), l);
    } else {
      if (min(x, y) >= b && max(x, y) >= l)
        cout << "YES\n";
      else
        cout << "NO\n";
    }
  }
  return 0;
}
