#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
bool cmp(pair<int, int> a, pair<int, int> b) { return a.second < b.second; }
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int t;
  cin >> t;
  int mx = -1, my = -1;
  while (t--) {
    char c;
    int t1, t2;
    cin >> c >> t1 >> t2;
    if (t1 > t2) swap(t1, t2);
    if (c == '+') {
      mx = max(mx, t1);
      my = max(my, t2);
    } else {
      if (mx <= t1 && my <= t2)
        cout << "YES\n";
      else
        cout << "NO\n";
    }
  }
  return 0;
}
