#include <bits/stdc++.h>
using namespace std;
int32_t main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long n;
  cin >> n;
  long long mxmx = -1, mnmx = -1;
  while (n--) {
    long long x, y, h, w;
    char c;
    cin >> c;
    if (c == '+') {
      cin >> x >> y;
      if (x < y) swap(x, y);
      mxmx = max(mxmx, x);
      mnmx = max(mnmx, y);
    } else {
      cin >> h >> w;
      if (max(h, w) >= mxmx && min(h, w) >= mnmx)
        cout << "YES"
             << "\n";
      else
        cout << "NO"
             << "\n";
    }
  }
  return 0;
}
