#include <bits/stdc++.h>
using namespace std;
const int MAXN = 100005;
const int MOD = 1000000007;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  int Q;
  cin >> Q;
  int mx1 = 0, mx2 = 0;
  while (Q--) {
    char op;
    int a, b;
    cin >> op >> a >> b;
    if (a > b) swap(a, b);
    if (op == '+') {
      mx1 = max(mx1, a);
      mx2 = max(mx2, b);
    } else {
      if (mx1 <= a && mx2 <= b) {
        cout << "YES\n";
      } else {
        cout << "NO\n";
      }
    }
  }
}
