#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long int t, x, y, xm, ym;
  char c;
  cin >> t;
  cin >> c >> x >> y;
  if (y > x) swap(x, y);
  xm = x;
  ym = y;
  t--;
  while (t--) {
    cin >> c >> x >> y;
    if (y > x) swap(x, y);
    if (c == '+') {
      if (xm < x) xm = x;
      if (ym < y) ym = y;
    } else {
      if (x < xm or y < ym)
        cout << "NO\n";
      else
        cout << "YES\n";
    }
  }
  return 0;
}
