#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(false);
  long long i, j, k, n, a, b, maxil = 0, maxiw = 0;
  char c;
  cin >> n;
  for (i = 0; i < n; i++) {
    cin >> c;
    if (c == '+') {
      cin >> a >> b;
      if (a > b) swap(a, b);
      maxil = max(maxil, b);
      maxiw = max(maxiw, a);
    }
    if (c == '?') {
      cin >> a >> b;
      if ((maxil <= a && maxiw <= b) || (maxil <= b && maxiw <= a)) {
        cout << "YES\n";
      } else {
        cout << "NO\n";
      }
    }
  }
}
