#include <bits/stdc++.h>
using namespace std;
using pii = pair<int, int>;
using ll = long long;
using pll = pair<long long, long long>;
using pil = pair<int, long long>;
using vi = vector<int>;
using vll = vector<long long>;
using vs = vector<string>;
using vc = vector<char>;
using vb = vector<bool>;
using vpii = vector<pair<int, int>>;
using vd = vector<double>;
using pil = pair<int, ll>;
using pli = pair<ll, int>;
using pdd = pair<double, double>;
using pss = pair<string, string>;
bool comp(pair<pii, int> a, pair<pii, int> b) {
  if (a.first.first == b.first.first) return a.first.second < b.first.second;
  return a.first.first < b.first.first;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie();
  cout.tie();
  int n;
  cin >> n;
  int e1 = 0, e2 = 0;
  for (int i = 0; i < n; i++) {
    char c;
    int x, y;
    cin >> c >> x >> y;
    if (c == '+') {
      e1 = max(e1, max(x, y));
      e2 = max(e2, min(x, y));
    } else {
      if (e1 <= x && e2 <= y || e1 <= y && e2 <= x) {
        cout << "YES"
             << "\n";
      } else
        cout << "NO\n";
    }
  }
  return 0;
}
