#include <bits/stdc++.h>
const int N = 200200;
const long long mod = 998244353;
using namespace std;
int n;
int main() {
  ios_base::sync_with_stdio(0);
  cin >> n;
  int a = 0, b = 0;
  for (int i = 1; i <= n; i++) {
    char c;
    int x, y;
    cin >> c >> x >> y;
    if (x > y) {
      swap(x, y);
    }
    if (c == '+') {
      a = max(a, x);
      b = max(b, y);
    } else {
      if (a <= x && b <= y) {
        cout << "YES"
             << "\n";
      } else {
        cout << "NO"
             << "\n";
      }
    }
  }
}
