#include <bits/stdc++.h>
using namespace std;
using ll = long long int;
using ld = long double;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  ll t = 1;
  while (t--) {
    int n;
    cin >> n;
    int h = 1, w = 1;
    for (int i = 0; i < n; i++) {
      char s;
      cin >> s;
      if (s == '+') {
        int x, y;
        cin >> x >> y;
        if (x > y) swap(x, y);
        h = max(h, x);
        w = max(w, y);
      } else if (s == '?') {
        int x, y;
        cin >> x >> y;
        if ((h <= x && w <= y) || (h <= y && w <= x))
          cout << "YES" << endl;
        else
          cout << "NO" << endl;
      }
    }
  }
  return 0;
}
