#include <bits/stdc++.h>
using namespace std;
int XX = -1, YY = -1;
int q;
int main() {
  ios::sync_with_stdio(0);
  cin >> q;
  for (int t = 1; t <= q; t++) {
    char s;
    cin >> s;
    int x, y;
    cin >> x >> y;
    int a = min(x, y);
    int b = max(x, y);
    x = a;
    y = b;
    if (s == '+') {
      XX = max(XX, x);
      YY = max(YY, y);
    } else {
      if (XX <= x && YY <= y)
        cout << "YES" << endl;
      else
        cout << "NO" << endl;
    }
  }
  return 0;
}
