#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long int n;
  cin >> n;
  long long int a = -1, b = -1;
  while (n--) {
    long long int aux1, aux2;
    char c;
    cin >> c >> aux1 >> aux2;
    if (aux1 < aux2) swap(aux1, aux2);
    if (c == '+') {
      a = max(a, aux1);
      b = max(b, aux2);
    } else {
      if (a <= aux1 && b <= aux2) {
        cout << "YES\n";
      } else
        cout << "NO\n";
    }
  }
  return 0;
}
