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