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