#include <bits/stdc++.h>
using namespace std;
const long long N = 1e5 + 5;
int32_t main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long t;
  cin >> t;
  multiset<long long> X, Y;
  while (t--) {
    char ty;
    cin >> ty;
    if (ty == '+') {
      long long x, y;
      cin >> x >> y;
      if (x > y) {
        swap(x, y);
      }
      X.insert(x);
      Y.insert(y);
    } else {
      long long h, w;
      cin >> h >> w;
      if (h > w) {
        swap(h, w);
      }
      auto it1 = X.upper_bound(h);
      auto it2 = Y.upper_bound(w);
      if (it1 == X.end() && it2 == Y.end()) {
        cout << "YES";
      } else {
        cout << "NO";
      }
      cout << endl;
    }
  }
}
