#include <bits/stdc++.h>
using namespace std;
int n, x, y, h, w, p, l, r;
int a, b;
int main() {
  ios::sync_with_stdio(false);
  cin >> n;
  a = b = p = 0;
  while (n--) {
    char t;
    cin >> t >> x >> y;
    if (t == '+') {
      if (x < y) {
        a = max(a, x);
        b = max(b, y);
      } else {
        a = max(a, y);
        b = max(b, x);
      }
      p++;
    }
    if (t == '?') {
      l = min(x, y);
      r = max(x, y);
      if (l >= a && r >= b)
        cout << "YES" << endl;
      else
        cout << "NO" << endl;
    }
  }
}
