#include <bits/stdc++.h>
using namespace std;
int32_t main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long t;
  cin >> t;
  long long maxx = 0, maxy = 0;
  pair<long long, long long> px, py;
  px.first = 0;
  px.second = 0;
  py.first = 0;
  py.second = 0;
  while (t--) {
    char c;
    long long x, y;
    cin >> c >> x >> y;
    long long x1 = min(x, y);
    long long y1 = max(x, y);
    x = x1;
    y = y1;
    if (c == '+') {
      maxx = max(x, maxx);
      maxy = max(maxy, y);
      if (x > px.first) {
        px.first = x;
        px.second = y;
      }
      if (y > py.second) {
        px.first = x;
        px.second = y;
      }
    } else {
      if (y >= maxy && x >= maxx)
        cout << "YES" << endl;
      else
        cout << "NO" << endl;
    }
  }
  return 0;
}
