#include <bits/stdc++.h>
using namespace std;
mt19937 rnd(1337);
const long long int INF = (long long int)1e18;
const long long int MOD = 1e9 + 7;
const long long int maxn = (long long int)1 * 1e5 + 10, L = 30;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  long long int n;
  cin >> n;
  long long int x = 0, y = 0;
  while (n--) {
    char wh;
    long long int a, b;
    cin >> wh >> a >> b;
    if (a > b) swap(a, b);
    if (wh == '+') {
      x = max(x, a);
      y = max(y, b);
    } else {
      if (x <= a && y <= b)
        cout << "YES\n";
      else
        cout << "NO\n";
    }
  }
  return 0;
}
