#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int n;
  cin >> n;
  long long x, y, mh = -1, mw = -1;
  char c;
  for (int i = 0; i < n; i++) {
    cin >> c >> x >> y;
    if (c == '+') {
      if (x > y) {
        mw = max(mw, x);
        mh = max(mh, y);
      } else {
        mw = max(mw, y);
        mh = max(mh, x);
      }
    } else {
      if (x > y) {
        if (mw <= x && mh <= y) {
          cout << "YES\n";
        } else {
          cout << "NO\n";
        }
      } else {
        if (mw <= y && mh <= x) {
          cout << "YES\n";
        } else {
          cout << "NO\n";
        }
      }
    }
  }
  return 0;
}
