#include <bits/stdc++.h>
using namespace std;
void solve() {
  long long int n, i, x, y, p, px = 0, py = 0;
  char j;
  cin >> n;
  while (n--) {
    cin >> j >> x >> y;
    if (j == '+') {
      if (y < x) {
        p = x;
        x = y;
        y = p;
      }
      px = max(px, x);
      py = max(py, y);
    } else if (j == '?') {
      if (y < x) {
        p = x;
        x = y;
        y = p;
      }
      if (px <= x && py <= y) {
        cout << "YES" << endl;
      } else {
        cout << "NO" << endl;
      }
    }
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long int t;
  t = 1;
  while (t--) {
    solve();
  }
}
