#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cin >> n;
  int a[n];
  long long l = 0, r = 0;
  for (int i = 0; i < n; i++) {
    char q;
    long long x, y;
    cin >> q >> x >> y;
    if (q == '+') {
      if (x > y) swap(x, y);
      l = (l > x) ? l : x;
      r = (r > y) ? r : y;
    } else {
      if (x > y) swap(x, y);
      if ((l <= x && r <= y))
        cout << "YES\n";
      else
        cout << "NO\n";
    }
  }
  return 0;
}
