#include <bits/stdc++.h>
using namespace std;
const long long inf = (long long)9e18;
const long long mod = (long long)1000000007;
struct cmp {
  bool operator()(const long long &i, const long long &j) const {
    return i > j;
  }
};
bool cmp1(pair<long long, long long> i, pair<long long, long long> j) {
  if (i.second != j.second)
    return i.second > j.second;
  else {
    return i.first > j.first;
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  long long n;
  cin >> n;
  long long mi1 = inf, mi2 = inf, ma1 = -1 * inf, ma2 = -1 * inf;
  for (long long i = 0; i < n; i++) {
    char c;
    cin >> c;
    if (c == '+') {
      long long l1, l2;
      long long a, b;
      cin >> a >> b;
      l1 = min(a, b);
      l2 = max(a, b);
      if (l1 > ma1) ma1 = l1;
      if (l2 > ma2) ma2 = l2;
    }
    if (c == '?') {
      long long z1, z2;
      cin >> z1 >> z2;
      long long d1 = min(z1, z2);
      long long d2 = max(z1, z2);
      if (d1 >= ma1 && d2 >= ma2) {
        cout << "YES" << '\n';
      } else {
        cout << "NO" << '\n';
      }
    }
  }
  return 0;
}
