#include <bits/stdc++.h>
using namespace std;
priority_queue<long long int, vector<long long int>, greater<long long int> > p;
unordered_map<long long int, long long int> um;
unordered_map<long long int, long long int>::iterator it;
vector<long long int> vect;
vector<long long int> v;
vector<pair<long long int, long long int> > vp;
set<long long int> st;
vector<long long int>::iterator upper1, upper2;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long int n, x, y;
  cin >> n;
  char kel;
  long long int mn = -1, mx = -1;
  while (n--) {
    cin >> kel >> x >> y;
    if (x > y) swap(x, y);
    if (kel == '+') {
      mn = max(mn, x);
      mx = max(mx, y);
    } else {
      if (x >= mn and y >= mx)
        cout << "YES" << endl;
      else
        cout << "NO" << endl;
    }
  }
}
