#include <bits/stdc++.h>
using namespace std;
long long int MOD = 998244353;
long long int INF = 1e18;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long int i, j, k, l, m, q, h, w, a, b;
  h = -1;
  w = -1;
  a = INF;
  b = -1;
  char s;
  cin >> q;
  while (q--) {
    cin >> s;
    if (s == '+') {
      cin >> k >> l;
      a = min(k, l);
      b = max(k, l);
      h = max(h, a);
      w = max(w, b);
    } else {
      cin >> k >> l;
      if (k >= h && l >= w || k >= w && l >= h) {
        cout << "YES" << endl;
      } else {
        cout << "NO" << endl;
      }
    }
  }
}
