#include <bits/stdc++.h>
using namespace std;
const int MAXN = (int)5e5;
int main() {
  int i, n;
  ios::sync_with_stdio(false);
  cin.tie(0), cout.tie(0);
  cin >> n;
  int a = 0, b = 0;
  for (i = 1; i <= n; i++) {
    int x, y;
    char ch;
    cin >> ch >> x >> y;
    if (x > y) {
      swap(x, y);
    }
    if (ch == '+') {
      a = max(a, x);
      b = max(b, y);
    } else {
      if (a <= x && b <= y) {
        cout << "YES"
             << "\n";
      } else {
        cout << "NO"
             << "\n";
      }
    }
  }
  return 0;
}
