#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int n;
  cin >> n;
  int xmax = 0, ymax = 0;
  for (int i = 0; i < n; i++) {
    char ch;
    int x, y;
    cin >> ch >> x >> y;
    if (y > x) swap(x, y);
    if (ch == '+') {
      xmax = max(xmax, x);
      ymax = max(ymax, y);
    } else if (ch == '?') {
      if ((x >= xmax && y >= ymax) || (x >= ymax && y >= xmax))
        cout << "YES" << endl;
      else
        cout << "NO" << endl;
    }
  }
}
